Marshall, who is currently 20 years old, is 4 times as old as his brother Stephen. How old will Stephen be when he is half a old as Marshall?

Answer 1

Marshall's age = M =20=4S 20 is 4 times Stephen's age

solve for S, divide by 4 S=20/4=5

then move ahead x years, when S is half M or M is twice S

M+x = 2(S+x)

20+x = 2(S+x)

20+x =2(5+x)

20+x =10+2x

x=10

S is 5 now. Add 10, he'll be 15 in 10 years

That's when Marshall will be 20+10=30 years old, which is twice 15

Answer: Stephen will be 15 when he's half as old as Marshall's 30 year age