Walkabout 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

We first want to create variables for Jack’s age today and Bill’s age today.

J =Jack’s age today

B = Bill’s age today

Now we can use these variables to set up two equations.

We are given that Jack is now 14 years older than Bill. This relationship is represented in our first equation.

J = B + 14 Eq (1)

Next we are given that in 10 years Jack will be twice as old as Bill. Remember, in setting up this equation we must add 10 years to both Jack's and Bill’s current ages, respectively.

10 + J = 2(B + 10)

10 + J = 2B + 20

J = 2B + 10 Eq (2)

Now we can set our two equations (Eq (1) and Eq (2)) equal to each other and determine the value of B.

B + 14 = 2B + 10

B = 4

This means that Bill’s age today is 4.

Thus, we know that Jack’s age today is 14 + 4 = 18.

This means that Jack’s age in 5 years will be 18 + 5 = 23.

Answer is D

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Jeffrey Miller

Jeffrey Miller

Head of GMAT Instruction