Three pupils each filled part of a bucket with sand. Ana filled 310 of her bucket, Ben filled 25 of his bucket and Cai filled 720 of his bucket.
- Write 310, 25 and 720 as fractions with denominator 20. [1 mark]
- Arrange the three names from the pupil who filled the most sand to the pupil who filled the least. [2 marks]
Need a hint?
Part (a): find a number that 10, 5 and 20 all divide into exactly. Part (b): once the denominators match, compare only the numerators.
Worked answer
- (a) 20 is a multiple of 10, 5 and 20, so use 20 as the common denominator.
- (a) 310 = 620, 25 = 820, 720 stays as 720.
- (b) Compare the numerators over the same denominator: 8 > 7 > 6.
- (b) So 25 is the greatest, then 720, then 310: Ben, Cai, Ana.
Answer: Ben, Cai, Ana
The mistake this question tests
Habit
Factors and multiples (HCF, LCM)
Comparing numerators without matching denominators (3, 2, 7 gives Cai, Ana, Ben) or comparing denominators (smaller denominator treated as greater) gives the wrong order.
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See the answer →Practise PSLE fractions until the mistakes stop.
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