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 7 years ago? Choose the correct choice from the following answers.
A) 8 B) 10 C) 12 D) 14 E) 7
Let's say   Age of Richard isR   Age of David isD   Age of Scott isS   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 7 years ago?   i.e. D-7 = 14-7= 
<gadget id="calculator">14-7</gadget>
<output>7</output>
7 years   Answer: Option   7
<result>E</result>
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 7 years ago?