MYP Math – The Examiner’s Handbook: Exam Traps Students Must Avoid - Part 2 | IBMytians Blog

IB MYP 5 · Mark Deduction Guide · IBmytians.com

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PURPOSE OF THIS GUIDE

This guide is for mathematically strong students who keep losing marks on things that feel "unfair" or "too picky."

If you understand the math but your score does not reflect that, read this document carefully.

Each trap below follows the same structure:

The ScenarioWhat a typical strong student writes.

The Student's ThinkingWhy they believe it is correct.

Why IB Deducts MarksThe hidden expectation.

What IB Expects InsteadA model answer.

Markscheme EvidenceThe exact IB wording that causes the deduction.

One-Sentence RuleThe key takeaway in a single line.

QUICK REFERENCE — THE 12 TRAPS AT A GLANCE

#	Trap Name	One-Sentence Rule
TRAP 1	Show That	The answer is given. You are marked on the path, not the destination.
TRAP 2	Verify	Calculate + compare + say "they match". All three are required.
TRAP 3	Describe in Words	Use full English sentences. No algebra. No single keywords.
TRAP 4	Justify	Answer "Why is this true?" not "What is the rule?"
TRAP 5	Notation Error	Copy the variable from the table. If it says n, write n.
TRAP 6	Additional Information	Give exactly what is asked. Not less. Not more.
TRAP 7	ECF	ECF helps only if you kept the same difficulty.
TRAP 8	Write Down Location	Your answer goes in the designated space. Not the margin.
TRAP 9	Probability Context	Write P(event) = value. Never just the number.
TRAP 10	Rounding Precision	Keep full precision. Round once at the end.
TRAP 11	Coordinates vs Values	If it says "coordinates", write (x, y).
TRAP 12	Terminology	Use the exact words from the markscheme. "Mutually exclusive" is safe.

Trap 1: The "Show That" Trap

You do the math correctly, but you skip steps because the answer seems obvious.

📋 The Scenario

The question asks: "Show that BC = 4 to the nearest unit." (Triangle with hypotenuse 9, one side 8)

You write:

BC = √(9² - 8²) = 4.12

🤔 The Student's Thinking

"I did the Pythagoras. The answer is 4.12, which rounds to 4. I showed it."

❌ Why IB Deducts Marks

The command term "show that" means the final answer is already given in the question. Your job is not to produce the answer. Your job is to demonstrate the reasoning that leads to it.

If you write only the final calculation and the rounded answer, the examiner cannot see:

That you knew which side is the hypotenuse
That you subtracted correctly (81 − 64)
That you took the square root
That you understood rounding

The markscheme splits "show that" into bullet points. Each bullet point must be visibly present. If you combine two steps into one line, you lose a mark.

✅ What IB Expects Instead

You must write every intermediate step separately:

BC 2 = AB 2 - AC 2 BC 2 = 9 2 - 8 2 BC 2 = 81 - 64 BC 2 = 17 BC = \sqrt 17 BC = 4.123\dots BC \approx 4 (to the nearest unit)

📜 Markscheme Evidence

"For 'show that' questions, unless otherwise noted, every bullet point has to be seen in order to be awarded."

"Seeing only √9² − 8² OE is only bp1. Seeing only 4.1(231...) is only bp2."

Trap 2: The "Verify" Trap

You test your rule, but you forget to say that it matches the table.

📋 The Scenario

You have derived the rule S = 4n for the number of sticks. The question asks: "Verify your general rule for S."

You write:

4 × 5 = 20

🤔 The Student's Thinking

"I substituted n = 5. I got 20. That is correct. I verified it."

❌ Why IB Deducts Marks

The command term "verify" means: check AND confirm.

If you only do the calculation, you have checked (step 1). But you have not confirmed that the result matches the expected value (step 2).

The confirmation statement is worth a separate mark. Without it, the examiner cannot be sure that you actually compared your result to the table or pattern.

✅ What IB Expects Instead

You must explicitly state that your result matches the known value:

Verifying for n = 5: S = 4 \times 5 = 20 This matches the value in the table (Stage 5 has 20 sticks). Therefore the rule is verified. ✓

Or more concisely but still explicit:

Verifying for n= 4, S = 4 \times 5 = 20, as seen in the table. ✓

⚠️ The "Test vs Verify" Distinction (Critical)

Command Term	What You Do	Which Values to Use
Test	Check your rule for values already given in the question	n ≤ 4 (the values in the table)
Verify	Check your rule for values you predicted by continuing the pattern	n ≥ 5 (values not originally given)

If you use n = 5 for "test", you are using the wrong range. If you use n = 4 for "verify", you are using the wrong range.

📜 Markscheme Evidence

"Recognize that their correctly calculated value of C is the same as the correctly predicted value. If they use n=5 or n=6 ACCEPT only if they say 'as seen in the table' or 'so the rule works'."

Trap 3: The "Describe in Words" Trap

You write the algebraic rule or a single keyword, but the question asks for a verbal description.

📋 The Scenario

The table shows: Stage 1 → 4 sticks, Stage 2 → 8 sticks, Stage 3 → 12 sticks.

The question asks: "Describe, in words, two patterns in the table for the number of sticks (S)."

You write:

Pattern 1: S = 4n
Pattern 2: Arithmetic

🤔 The Student's Thinking

"The rule is 4n. That describes the pattern perfectly. And 'arithmetic' is a valid description."

❌ Why IB Deducts Marks

The phrase "in words" is a direct instruction. It means:

No algebraic symbols (=, n, 4n are not words)
No single keywords ('arithmetic' is a term, not a sentence)

IB expects complete English sentences that describe what is happening to the numbers. Writing S = 4n is mathematically correct, but it violates the instruction. The examiner will not award the mark.

✅ What IB Expects Instead

Write two complete sentences, one for each pattern:

Pattern 1: The number of sticks increases by 4 each stage. Or best — The number of sticks increases by 4 at each stage, so it follows an arithmetic sequence with a common difference of 4. Pattern 2: All values are multiples of 4.

Or:

Pattern 1: The difference between consecutive terms is constant at 4. Or best — The number of sticks increases by 4 at each stage, so it follows an arithmetic sequence with a common difference of 4. Pattern 2: Each stage number multiplied by 4 gives the number of sticks.

📜 Accepted vs Not Accepted

What You Write	Accepted?	Why
`S = 4n`	❌ No	Algebraic rule, not words
`Arithmetic`	❌ No	Single keyword, not a sentence
Increases by 4	✅ Yes	Complete idea (verb + number)
The values are even	✅ Yes	Complete sentence
Multiples of 4	✅ Yes	Acceptable as a phrase
The second difference is zero	✅ Yes	Complete sentence

"DO NOT ACCEPT the rule in words or description related to n for example: 4 times n, n multiplied by 4, WTTE."

"DO NOT ACCEPT incomplete description, for example: Arithmetic, linear, increasing by a constant."

Trap 4: The "Justify" Trap

You state the correct rule, but you do not explain where it comes from.

📋 The Scenario

You have discovered that T = n² + 3n for the total number of sticks. The question asks: "Justify your general rule for T."

You write:

T = n² + 3n

🤔 The Student's Thinking

"That is the rule. I found it. That is my justification."

❌ Why IB Deducts Marks

The command term "justify" means: give reasons or evidence to support your claim.

Stating the rule is not a justification. It is the claim itself. You need to explain why the rule is true.

IB distinguishes between:

Testing — checking that the rule works for some values
Verifying — checking that it works for predicted values
Justifying — explaining the mathematical or geometric reasoning behind the rule

If you only substitute numbers, you are testing or verifying, not justifying.

✅ What IB Expects Instead

You must explain the derivation of the rule.

For the sticks problem, the correct justification is:

Total sticks T = external sticks (S) + internal sticks (L) From earlier parts: S = 4 n L = n 2 - n Therefore: T = (n 2 - n) + 4 n T = n 2 + 3 n ✓

For a geometric pattern (like cube structures), the justification might be:

The structure is made of two parts: - The outer layer has 4 n + 1 cubes (from part d) - The top layer adds n 2 cubes Therefore total V = n 2 + 4 n + 1 ✓

📜 Levels of Justification (From Markschemes)

Level	What You Do	Marks
J1 (Weak)	Say "I used a quadratic model" or "I added two sequences"	1
J2 (Good)	Correctly substitute rules for M and N into Pythagoras, or correctly add S and L	2
J3 (Strong)	Complete simplification showing the final rule with geometric reasoning	3–4

"ACCEPT only if they have the general rule for V. Recognize the three terms 1, 4, 9 OE are added to the sequence C."

"Correctly justify the general rule for L geometrically using the rules for M and N into Pythagoras."

Trap 5: The "Notation Error" Trap (Using x instead of n)

You write the correct rule, but you use the wrong variable name.

📋 The Scenario

The table uses n for the stage number. You write the rule:

S = 4x

🤔 The Student's Thinking

"x is just a variable. It means the same thing as n. The math is identical."

❌ Why IB Deducts Marks

IB is strict about notation in final answers. The table explicitly uses n. The question asks for a rule "in terms of n". Using x is a notation error, even though the mathematics is identical.

This is not about mathematical correctness. It is about following the conventions of the question.

✅ What IB Expects Instead

Always use the exact variable that appears in the table or question:

S = 4 n

📜 Other Notation Errors That Lose Marks

What You Write	Why It Is Wrong	What IB Expects
`4*n`	Using * for multiplication in final answer	4n
`n^2`	Using ^ for power in final answer	n²
`√n²+4/4`	Missing brackets, ambiguous	√n² + 44
`U_n`	Using a different letter without defining it	T_n or state "let T = U_n"

"The following are considered errors in notation: using * for multiplication, using / for division, using ^ for power, using x instead of n, using U_n instead of T without mentioning that T = U_n."

Trap 6: The "Additional Information" Trap

You give the correct answer, but you add extra correct information that makes the answer incorrect.

📋 The Scenario

The question asks: "Write down the missing statistical term in the following statement."

The statement is: "The _____ is a measure of central tendency."

You know that median, mean, and mode are all measures of central tendency. You write:

median and mean

🤔 The Student's Thinking

"Both are correct. I am showing I know more."

❌ Why IB Deducts Marks

The question explicitly asks for "the missing statistical term" (singular). The blank in the sentence expects one word.

By writing two terms, you have:

Ignored the instruction (singular)
Made the sentence grammatically incorrect (cannot insert two terms into one blank)

The examiner will mark this as incorrect, even though both terms are mathematically correct measures of central tendency.

✅ What IB Expects Instead

Write only one term:

median

Or:

mean

Or:

mode

⚠️ The Same Trap Appears in Pattern Descriptions

If a question asks for "two patterns", do not write three. If you write three patterns and one of them is incorrect, you may lose marks even though you had two correct ones.

📜 Markscheme Evidence

"DO NOT ACCEPT if additional statistic is mentioned. Ex: median and LQ."

Trap 7: The "ECF" Trap (Error Carried Forward is NOT automatic)

You make an early mistake, but you do everything else perfectly. You assume you will get full credit for the rest.

📋 The Scenario

In part (a), you are asked to find the length AB using Pythagoras. You incorrectly add instead:

AB = 12 + 6 = 18

In part (b), you are asked to find the area of a circle with diameter AB. You correctly calculate:

Radius = 18 ÷ 2 = 9
Area = π × 9² = 81π

🤔 The Student's Thinking

"My part (a) was wrong, but my part (b) working is perfectly correct using my answer from (a). I should get ECF marks."

❌ Why IB May NOT Award ECF

The markscheme has a specific rule: ECF may not be fully awarded if the error transforms the question into a simpler one.

In this case:

The original part (a) required Pythagoras theorem (a non-trivial skill)
Your error turned it into simple addition (a trivial skill)
You avoided the difficult part of the question entirely

IB considers this an unfair advantage. ECF is reduced or not awarded.

✅ When ECF Is Awarded (And When It Is Not)

Scenario	ECF Awarded?
You use Pythagoras but mis-square a number (e.g., 12² = 140). Subsequent working is correct.	✅ Yes (same complexity)
You add instead of using Pythagoras.	❌ No (simpler question)
You use the wrong formula but the complexity is similar.	⚠️ Possibly, examiner discretion
You make a second error after the first.	❌ No (ECF stops at second error)
You do not show any working in the subsequent part.	❌ No (working required for ECF)

📜 The Full List of ECF Conditions (From Markscheme)

Working must be present for the part.
All working subsequent to the error must be correct.
The error must not transform the question into a simpler question.
The answer must be appropriate (no negative distances, no sin x > 1).

"If a question is transformed by an error into a simpler question then ECF may not be fully awarded."

Trap 8: The "Write Down" Trap (Location matters)

You calculate the correct answer, but you write it in the margin instead of in the designated space.

📋 The Scenario

The question shows a Venn diagram with blank spaces. You calculate the missing values: 8, 7, 5, 4.

You write at the bottom of the page:

8, 7, 5, 4

🤔 The Student's Thinking

"The numbers are correct. The examiner can see them. That should be fine."

❌ Why IB Deducts Marks

The phrase "write down" in IB examinations often implies "write in the space provided."

If there is a table, a diagram, or blanks in the question, those are where the answer belongs. Writing elsewhere forces the examiner to search for your answer. In on-screen examinations, the answer may be automatically marked by the system, and the system only checks the designated input areas.

✅ What IB Expects Instead

Place each value directly into the correct location on the diagram:

The number 8 in the "Guitar only" region
The number 7 in the intersection region
The number 5 in the "Drums only" region
The number 4 in the "Neither" region

📜 Markscheme Evidence

"Correctly write one value in the Venn diagram. Correctly write another two values."

Note that the markscheme specifies "in the Venn diagram" — not anywhere on the page.

Trap 9: The "Probability Context" Trap

You write the correct fraction or decimal, but you do not indicate that it is a probability.

📋 The Scenario

The question asks: "Determine the probability that the sum of the two numbers is a prime number."

You calculate 6 favorable outcomes out of 16 total. You write:

6/16

🤔 The Student's Thinking

"The question asked for probability. 6/16 is clearly the probability. I don't need to say it again."

❌ Why IB Deducts Marks

While 6/16 is mathematically the correct probability, IB expects context in probability answers. The examiner should not have to infer what your number represents.

In longer questions with multiple parts, a number alone could be the answer to part (a), part (b), or an intermediate calculation. Writing P(prime) = 6/16 removes all ambiguity.

✅ What IB Expects Instead

Write the probability with a clear statement:

P(prime) = 616 = 38

Or:

The probability is 616 = 38

Or:

The probability is 616 (which simplifies to 38)

📜 Markscheme Evidence

The markscheme often says: "their 6/16 award 2 marks" — meaning the number alone is accepted. However, this is a minimum acceptance, not the model answer. To be safe, always add context.

Trap 10: The "Rounding Precision" Trap

You round an intermediate value, then use that rounded value in further calculations.

📋 The Scenario

You are calculating the height of a triangle using tan 70° = h / 1100.

Your calculator shows: tan 70° = 2.747477419…

You write: tan 70° = 2.747

Then: h = 2.747 × 1100 = 3021.7

🤔 The Student's Thinking

"2.747 is accurate enough. The answer is still close to 3022."

❌ Why IB Deducts Marks

The markscheme for "show that" questions requires the unrounded value before rounding. Using a rounded intermediate value can cause the final answer to be slightly off.

In this case, 2.747 × 1100 = 3021.7 rounds to 3022, so it is accepted. But if the rounding caused the final answer to be 3021.4, it would round to 3021, and you would lose the mark.

The safe approach is to use full calculator precision for all intermediate steps.

✅ What IB Expects Instead

Keep the value in your calculator. Do not round until the final step:

h = 1100 \times tan 70° h = 1100 \times 2.747477419\dots h = 3022.225\dots h \approx 3022 m (to the nearest metre)

📜 Common Rounding Errors & Markscheme Evidence

Error	Why It Is Wrong
Rounding tan 70° to 2.75	Too much rounding; final answer may be 3025
Rounding √17 to 4.12, then using 4.12 in area calculation	Cumulative rounding error
Writing 2.586 as 2.6 (correct) but then using 2.6 to calculate something else	Acceptable only if the final answer still rounds correctly
Not rounding to the required precision at the end (e.g., leaving 4.12 when "nearest unit" is asked)	Missing the rounding instruction

"ACCEPT using rounded trig ratio only if the value of h rounds to 3022."

"DO NOT ACCEPT if their result does not need rounding."

Trap 11: The "Coordinates vs Values" Trap

You calculate the correct x-value of an intercept, but you forget to write it as a coordinate pair.

📋 The Scenario

The question asks: "Calculate the coordinates of the x-intercepts of the parabola."

You solve ½(x − 4)² − 1 = 0 and get x = 2.6 and x = 5.4.

You write:

2.6 and 5.4

🤔 The Student's Thinking

"Those are the x-intercepts. The y-coordinate is zero, so that is obvious. I don't need to write (2.6, 0)."

❌ Why IB Deducts Marks

The question explicitly asks for "coordinates" (plural of coordinate). A coordinate is an ordered pair: (x, y).

Writing only the x-value is incomplete. The examiner cannot be sure that you remember the y-coordinate is zero. In coordinate geometry questions, the format matters.

✅ What IB Expects Instead

Write the full coordinate pairs:

(2.6, 0) and (5.4, 0)

📜 The Same Trap in Other Contexts

Question Asks For	What You Write (Wrong)	What IB Expects
Coordinates of point A	x = 3, y = 4	(3, 4) or A(3, 4)
y-coordinate of point B	16	y = 16 or y_B = 16
The vertex of the parabola	x = 4	(4, −1) or "vertex at (4, −1)"

"(2.6, 0) AND (5.4, 0) ACCEPT 2.6 and 5.4"

Note: The markscheme accepts just the numbers, but this is a minimum. To be safe, always write the full coordinates.

Trap 12: The "Mutually Exclusive" Terminology Trap

You correctly understand that two events cannot happen together, but you use the wrong mathematical term.

📋 The Scenario

The question shows a sample space and states: "P(R ∩ S) = 0 because event R and event S are _____ events."

You know that R and S cannot happen at the same time. You write:

not overlapping

🤔 The Student's Thinking

"Not overlapping means they don't share any outcomes. That is correct."

❌ Why IB Deducts Marks

IB has a specific list of accepted terms for this concept. "Not overlapping" is not on the list. The examiner is instructed not to accept it, even though the meaning is clear.

This is a vocabulary test as much as a math test. You must use the precise mathematical terminology that IB expects.

✅ What IB Expects Instead

Any of these three terms:

disjoint

incompatible

mutually exclusive

"Mutually exclusive" is the most common and is always accepted.

📜 Terms That Are NOT Accepted (Even If They Make Sense)

What You Write	Why Not Accepted
not overlapping	Not on the accepted list
opposing	Not on the accepted list
non-related	Not on the accepted list
not simultaneous	Not on the accepted list
independent	This is a different concept — P(A ∩ B) = P(A) · P(B)

"ACCEPT disjoint or incompatible or non-compatible. DO NOT ACCEPT other descriptions. Ex: not simultaneous, not overlapping, opposing, non-related, not intersecting,...etc"

FINAL CHECKLIST — BEFORE YOU SUBMIT

For "Show That" Questions

Did I write every intermediate step separately?

Is each bullet point from the markscheme visible in my working?

For "Verify" Questions

Did I use n ≥ 5 (predicted values)?

Did I explicitly state that my result matches the table or pattern?

For "Describe in Words" Questions

Did I avoid algebraic symbols (=, n, 4n)?

Did I write complete English sentences?

Did I avoid single keywords like "arithmetic" or "linear"?

For "Justify" Questions

Did I explain where the rule comes from?

Did I use geometric reasoning or algebraic derivation?

Did I avoid just restating the rule?

For Notation

Did I use the same variable as the table (usually n)?

Did I avoid *, /, ^ in final answers?

Did I use proper brackets to avoid ambiguity?

For General Presentation

Is my answer in the designated space (table, diagram, blank)?

Did I write probabilities as P(event) = value?

Did I keep full precision and round only at the end?

Did I write coordinates as (x, y) when asked?

Did I use accepted terminology (mutually exclusive, not "not overlapping")?

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MYP Math – The Examiner’s Handbook: Exam Traps Students Must Avoid - Part 2

Hidden Mark Loss: When Correct Answers Still Lose Marks

PURPOSE OF THIS GUIDE

QUICK REFERENCE — THE 12 TRAPS AT A GLANCE

FINAL CHECKLIST — BEFORE YOU SUBMIT

For "Show That" Questions

For "Verify" Questions

For "Describe in Words" Questions

For "Justify" Questions

For Notation

For General Presentation