Dev has some bread rolls for a neighbourhood event. He can pack all of them into bags of 10 with none left over. He can also pack all of them into bags of 15 with none left over. He has fewer than 70 bread rolls. Write down all the possible numbers of bread rolls he has.
Need a hint?
List the multiples of 15 below 70. Which of them can also be packed into bags of 10?
Worked answer
- The number of rolls must be a multiple of 10 and also a multiple of 15.
- Multiples of 15 below 70: 15, 30, 45, 60.
- 15 and 45 are not multiples of 10. 30 and 60 are.
- Dev could have 30, 60 bread rolls.
Answer: 30, 60 bread rolls
The mistake this question tests
Habit
Factors and multiples (HCF, LCM)
Some pupils list every multiple of 10 below 70 (10, 20, 30, 40, 50, 60) without checking that each can also be packed into bags of 15.
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See the answer →Practise PSLE whole numbers until the mistakes stop.
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