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Applied problems

by pullagurla » Thu Sep 02, 2010 10:37 pm
Jack is now 14 years older than Bill. If in 10 years Jack
will be twice as old as Bill, how old will Jack be in
5 years?
(A) 9
(B) 19
(C) 21
(D) 23
(E) 33

Explain by backsolving
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by Rahul@gurome » Fri Sep 03, 2010 3:31 am
pullagurla wrote:Jack is now 14 years older than Bill. If in 10 years Jack will be twice as old as Bill, how old will Jack be in 5 years?
(A) 9
(B) 19
(C) 21
(D) 23
(E) 33

Explain by backsolving
Let Jack's present age = J and Bill's age = B
Start from option (E), after 5 years J will be 33 implies now J = 28 and B = 14. Now after 10 years J + 10 = 2(B + 10), we need to check this. After 10 years J = 38 and B = 24 and 38 is not two times 24. So, this is not the correct answer.

Now we check option (D), after 5 years J will be 23 implies now J = 18 and B = 4. Now after 10 years J + 10 = 2(B + 10), we need to check this. After 10 years J = 28 and B = 14 and 28 is two times 14. So, this is the correct answer.

The correct answer is [spoiler](D)[/spoiler].
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