Judy is 26 years old and Diane is 5 years old. In how many years will Judy be twice as old as Diane?

[BTGModeratorVI]

Judy is 26 years old and Diane is 5 years old. In how many years will Judy be twice as old as Diane?

A. 16
B. 19
C. 21
D. 24
E. 26

Answer: A
Source: Princeton Review

[Brent@GMATPrepNow]

Judy is 26 years old and Diane is 5 years old. In how many years will Judy be twice as old as Diane?

A. 16
B. 19
C. 21
D. 24
E. 26

Answer: A
Source: Princeton Review

Let x = the number of years until Judy is twice as old as Diane

So, 26 + x = Judy's age in x years
And 5 + x = Diane's age in x years

We get the equation: 26 + x = 2(5 + x)
Expand: 26 + x = 10 + 2x
Subtract x from both sides: 26 = 10 + x
Subtract 10 from both sides: 16 = x

Answer: A