Fraction problem

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Fraction problem

by princessss » Thu Oct 07, 2010 2:52 am
Alices' take home - pay last year was the same each month, and she saved the same praction of her take - home pay each month. The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take - home pay that she didn't save. If all the money that she saved last year was from her take - home pay. what fraction of her take - home pay did she save each month?

Please help, I always get 1/4 and 1/5 is the correct answer. I don't know what I'm doing wrong.
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by kmittal82 » Thu Oct 07, 2010 3:11 am
Let monthly take home pay = x, saving = 1/y

So, she saves (1/y)*x = x/y every month

>The total amount of money that she had saved at the end of the year
12x/y

>3 times the amount of that portion of her monthly take - home pay that she didn't save
3(x-x/y)

Thus, 12x/y = 3[x - (x/y)]

Solve to get y = 5, thus saving = 1/5

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by GMATGuruNY » Thu Oct 07, 2010 3:12 am
Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month. The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save. If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

a. 1/2
b. 1/3
c. 1/4
d. 1/5
e. 1/6


When you post a question, please include the answer choices.

This is a great question for plugging in the answers, which represent the fraction saved each month.

Plug in monthly pay = 60. (60 is a good number because it's divisible by all the denominators in the answer choices.)

Answer choice C: 1/4 saved each month

1/4 * 60 = 15 saved each month, 45 not saved.
12*15 = 180 total saved for the whole year.
(Total saved)/(monthly not saved) = 180/45 = 4. We need her to save less.

Answer choice D: 1/5 saved each month

1/5 * 60 = 12 saved each month, 48 not saved.
12*12 = 144 total saved for the whole year.
(Total saved)/(monthly not saved) = 144/48 = 3. Success!

The correct answer is D.
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