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P5 maths fraction multiplication paper 4 (error review): the commonest slips
P5 maths fraction multiplication paper 4 (error review): the commonest slips
Ten items aimed at the commonest calculation slips: spot the mistake first, then work out the right answer.
Direct answers Read the mistake in each item, decide why it is wrong, then check the answer table in section 03.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: P5 Maths Multiplying Fractions |
| Level | P5 |
02 Questions (10 items)
- FoundationA pupil multiplied the denominator too and wrote 20/35 for 4/7 × 5. What is the correct answer?
- FoundationWork out 9/10 × 4.
- FoundationWork out 3/8 × 6.
- IntermediateWork out 2 1/3 × 3/7.
- IntermediateWork out 4/5 × 15/16.
- IntermediateWork out 1 5/8 × 2 2/13.
- ChallengeOne parcel weighs 5/6 kg. What is the total mass of 24 such parcels?
- ChallengeA class of 42 pupils is 3/7 boys. How many girls are there?
- ChallengeA rope is 3 3/4 m long and 4/5 of it is used. How many metres are used?
- Error redoA pupil worked out 2 1/2 × 1 1/2 as 2 × 1 + 1/2 × 1/2 = 2 1/4. What is the correct answer?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 20/7, that is 2 6/7 | With a whole number the denominator does not change and only the numerator 4 × 5 = 20 is multiplied, giving 20/7; 20/35 simplifies to 4/7, which is the wrong value. |
| 2 | 18/5, that is 3 3/5 | The numerator becomes 9 × 4 = 36 over the same 10, and 36/10 simplifies to 18/5. |
| 3 | 9/4, that is 2 1/4 | Cancel first: 6 and 8 share 2, leaving 3 and 4, so 3 × 3/4 = 9/4. |
| 4 | 1 | Change 2 1/3 to 7/3; it cancels completely with 3/7, leaving 1. |
| 5 | 3/4 | Cancel 4 with 16 and 5 with 15 to leave 1 × 3/4, that is 3/4. |
| 6 | 7/2, that is 3 1/2 | As 13/8 and 28/13 the thirteens cancel, and 28/8 simplifies to 7/2. |
| 7 | 20 kg | Each parcel is 5/6 kg, so 5/6 × 24 = 120/6 = 20 kg. |
| 8 | 24 girls | Boys are 42 × 3/7 = 18, so girls are 42 − 18 = 24, which is also 42 × 4/7. |
| 9 | 3 m | 3 3/4 is 15/4, and 15/4 × 4/5 = 60/20 = 3 m, leaving 3 3/4 − 3 = 3/4 m. |
| 10 | 15/4, that is 3 3/4 | Each mixed number must become improper: 5/2 × 3/2 = 15/4; multiplying whole parts and fraction parts separately loses 2 × 1/2 and 1 × 1/2. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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