The ratio of the number of pupils in Class A to the number of pupils in Class B is 2:5. The ratio of the pupils in Class B to the number of pupils in Class C is 10:3.

Question

a. Find the ratio of the number of pupils in Class A to the number of pupils in Class B to the number of pupils in Class C.
b. If there are 70 pupils in Class A and Class C altogether, how many pupils are there in Class B?
c. If Class B has 40 pupils, how many pupils are there in Class A and Class C altogether?

Answer 1

A : B = 2 : 5 or 4 : 10 (looking at the next line)
B : C = 10 : 3

so A : B : C = 4 : 10 : 3

b)

A : C = 10 : 3
so 3A = 10C ---> A = 10C/3
also A+C = 70
12C/3 + C = 70
12C + 3C = 210
15C = 210
C = 14
B = 56

c) I assume we go back to the original definition, and the count is different from b)
A : B : C = 4:10:3
A:40:C = 4:10:3 = 16:40:12
Then A 16 , C=12
A+C = 28