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


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


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


Nicholas Dureault

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

so we get:

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

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)

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

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Official Guide for the GMAT 2015 14th Ed.

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Official Guide for the GMAT 12th Ed.

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Section 5.3 Problem Solving

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