Today Rebecca, who is 34 years old, and her daughter, who is

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swerve: Legendary Member; Posts: 2548; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Tue Aug 20, 2019 2:23 pm

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Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca's age is twice her daughter's age?

A. 10
B. 14
C. 18
D. 22
E. 26

The OA is C

Source: Official Guide

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Source: Beat The GMAT — Problem Solving | Tue Aug 20, 2019 2:23 pm

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Aug 20, 2019 2:34 pm

swerve wrote:Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca's age is twice her daughter's age?

A. 10
B. 14
C. 18
D. 22
E. 26

The OA is C

Source: Official Guide

I think the best (i.e., fastest) approach is to TEST the answer choices.
However, for those who prefer using algebra, here's an algebraic approach:

Let x be the number of years from today.
So, x years in the future, Rebecca's age will be 34 + x
And, x years in the future, her daughter's age will be 8 + x

We want Rebecca's future age to be twice her daughter's future age.
We can create the following "word equation": (Rebecca's future age) = 2(daughter's future age)
Or we can write: (34 + x) = 2(8 + x)
Expand to get: 34 + x = 16 + 2x
Solve to get: x = 18

Answer: C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Sun Aug 25, 2019 5:25 pm

swerve wrote:Today Rebecca, who is 34 years old, and her daughter, who is 8 years old, celebrate their birthdays. How many years will pass before Rebecca's age is twice her daughter's age?

A. 10
B. 14
C. 18
D. 22
E. 26

The OA is C

Source: Official Guide

We are given that Rebecca is 34 and her daughter is 8. We can let n = the number of years until Rebecca is twice as old as her daughter. At that time, Rebecca will be (34 + n) years old, and her daughter will be (8 + n) years old, and Rebecca will be twice her daughter's age:

34 + n = 2(8 + n)

34 + n = 16 + 2n

18 = n

Answer: C

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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