Find the missing number in the box. 5 : 7 = ? : 42
Need a hint?
Work out what number you multiply 7 by to get 42, then multiply 5 by the same number.
Worked answer
- Find the multiplier from the second part: 42 ÷ 7 = 6
- Multiply the first part by the same multiplier: 5 × 6 = 30
- So 5 : 7 = 30 : 42
Answer: 30
The mistake this question tests
Habit
Stopped at one part in ratio
Pupils often add instead of multiply. They see 7 + 35 = 42 and wrongly do 5 + 35 = 40.
How to fix it at home →Wrong answers children often give:
- 6 Stopped at one part in ratio
- 35 Stopped at one part in ratio
- 40 Calculation slip
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See the answer →Practise PSLE ratio until the mistakes stop.
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