Question

If A : B = 3 : 5 and B : C = 4 : 7 , find A : B : C.

Answer 1

A : B = 3 : 5 = 12 : 20
B : C = 4 : 7 = 20 : 35

Observe that the figures against b are 5 &4

Find LCM of 5 and 4.
This is 20.

Therefore,a:b=(multiply by 4)3×4 : 5×4 =12:20

B:C=(multiply by 5)4×5:7×5=20:35

When figure against b is made same (as b=20)

Therefore A : B : C = 12 : 20 : 35