My younger brother needs help understanding this Math problem, how can I help him understand this?

Question

A ski group rented a bus to the ski slopes. Only 7/10 of the group went on the trip and only 3/5 of those paid in advance. What part of the total group paid in advance?

(A) 14/3

(B) 21/50

(C) 2/3

(D) 6/7

Answer 1

3/5 of the 7/10 on the bus paid in advance:

Fraction that paid in advance = (3/5)·(7/10) = _____?

Answer 2

To understand the concept, use simple numbers. If (say) 12 were in the ski group and half went on the bus, that means 6 went on the bus (1/2 times 12 equals 6). If a third of the bus group paid in advance, that means 2 paid (1/3 times 6 equals 2). So multiply the two fractions together and get 1/6 and see that 1/6 of 12 is 2. So you know you can do the same with this problem: 3/5 times 7/10 gives you the answer. Fun!