P5 Math problem sums

Question

Class A hadf 8 more pupils than Class B. During an outing,40%of the pupilsfrom Class A and 75% of the pupils from Class B went cycling.The remaining pupils stayed at the playground.There are thrice as many pupils from Class A than those from Class B that stayed at the playground.How many pupils were there in Class A?

 

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Answer 1

Let the number of pupils in class B be b. Then the number of pupils in class A is b+8. 40% is 2/5 and 75% is 3/4. 3/5 (60%) of class A=3(b+8)/5; 1/4 (25%) of class B=b/4. These pupils stayed in the playground. 3(b+8)/5=3b/4, because three times as many from class A stayed as those in class B. So (b+8)/5=b/4. Multiply both sides by 20: 4b+32=5b, so b=32. Therefore the number of pupils in class A = 32+8=40.

Checks: 60% of class A is 3/5*40=24; 25% of class B is 1/4*32=8. So there were 3 times as many from class A as class B. 40% of class A=16; 75% of class B=24. 40 pupils went cycling and 32 stayed. Total number of pupils=40+32=72.