P, Q and R are 2-digit numbers. The average of these 3 numbers is 38. The value of P is 24. The value of Q is 5 times the value of R. Find the value of Q.
- Find the total of the 3 numbers.
- Find the value of Q.
Need a hint?
First find the total of all 3 numbers using the average. Then subtract P to get Q + R. Since Q is 5 times R, you can use 6 equal units.
Worked answer
- Total of 3 numbers = 38 × 3 = 114
- Q + R = 114 − 24 = 90
- Q = 5 × R, so Q + R = 6 units = 90
- 1 unit = 90 ÷ 6 = 15
- Q = 5 units = 5 × 15 = 75
Answer: 75
The mistake this question tests
Habit
Average and total
Pupils often forget to multiply the average by 3 and use 38 as the total, or they divide 90 by 5 instead of 6.
How to fix it at home →Wrong answers children often give:
- 15 Stopped at one part in ratio
- 18 Stopped at one part in ratio
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See the answer →Practise PSLE whole numbers until the mistakes stop.
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