Source: Official Guide for GMAT Review 2016 Problem Solving; #3

15

Today Rebecca, who is 34 years old

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?

2 Explanations

1

Nicola Key

You can back solve by by substituting the answers choices and till you get the one that works out.

Jun 11, 2017 • Comment

6

Nicholas Dureault

Let 'x' equal the amount of years to pass.

so we get:

34 + x
-------- = 8 + x
2

Since we are looking for Rebecca to be twice her daughters age, we need to divide her future age (current age + 'x') by '2' in order for the equation to balance.
(This is where I originally was hung up in creating the equation, I didn't know what to do with the "twice her daughter's age" part).

We can move the denominator '2' by multiplying both sides by 2 and you get:
34 + x = 2(8 + x)

Simplify:
34 + x = 16 + 2x

move the x's over to one side and the numbers over to the other:
34 - 16 = 2x - x

Simplify and solve:
18 = x

Dec 19, 2015 • Comment

Cydney Seigerman, Magoosh Tutor

Great job! Thanks for sharing your solution :)

Dec 21, 2015 • Reply

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Official Guide for GMAT Review 2016

Official Guide for the GMAT 2015 14th Ed.

Official Guide for the GMAT 13th Ed.

Official Guide for the GMAT 12th Ed.

Revised GRE PDF 2nd Ed.


Section 5.3 Problem Solving

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