Stardust Chris wrote:

A certain family has 3 sons: Richard is 6 years older than David, and David is 8 years older than Scott. If in 8 years, Richard will be twice as old as Scott, then how old was David 4 years ago?

(A) 8

(B) 10

(C) 12

(D) 14

(E) 16

Let's say

Age of Richard is "R"

Age of David is "D"

Age of Scott is "S"

Now

Richard is 6 years older than David,

i.e. R = D +6

David is 8 years older than Scott

i.e. D = S +8

If in 8 years, Richard will be twice as old as Scott

i.e. R+8 = 2x(S+8)

i.e. R+8 = 2S + 16

i.e. R = 2S+8

But R = D+6 = (S+8)+6 = S+14

therefore, 2S + 8 = S +14

i.e. S = 6

i.e. R = 20

i.e. D = 14

Now,

how old was David 4 years ago?

i.e. D-4 = 14-4 = 10 years

Answer: Option

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