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Andre has already saved 3/7 of the cost of a new car...

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Andre has already saved 3/7 of the cost of a new car...

by swerve » Tue Jan 23, 2018 5:22 am
Andre has already saved 3/7 of the cost of a new car, and he has calculated that he will be able to save 2/5 of the remaining amount before the end of the summer. If his calculations are correct, what fraction of the cost of the new car will he still need to save at the end of summer vacation?

A. 6/36
B. 8/35
C. 12/35
D. 23/35
E. 29/35

The OA is C.

Please, can any expert explain this PS question for me? I can't get the correct answer.

I know that he saved 3/7 of the cost, that's mean that the remaining amount will be 4/7. The he has calculated that he will be able to save 2/5 of the remaining amount, that's mean 2/5 of the 4/7.

I stuck here. I need your help, please. Thanks.
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by GMATGuruNY » Tue Jan 23, 2018 5:44 am
swerve wrote:Andre has already saved 3/7 of the cost of a new car, and he has calculated that he will be able to save 2/5 of the remaining amount before the end of the summer. If his calculations are correct, what fraction of the cost of the new car will he still need to save at the end of summer vacation?

A. 6/36
B. 8/35
C. 12/35
D. 23/35
E. 29/35
Let the total cost = the LCM of the two denominators = 7*5 = 35.

Since Andre has already saved 3/7 of the total cost, the amount already saved = (3/7)(35) = 15.

Remaining amount to be saved = 35-15 = 20.
Since Andre will save 2/5 of the remaining amount by summer's end, the additional amount that will be saved by summer's end = (2/5)(20) = 8.

Total saved = 15+8 = 23.
Remaining amount to be saved = (total cost) - (amount saved) = 35-23 = 12.
Resulting fraction:
(remaining amount to be saved)/(total cost) = 12/35.

The correct answer is C.
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by Jeff@TargetTestPrep » Fri Jan 26, 2018 12:28 pm
swerve wrote:Andre has already saved 3/7 of the cost of a new car, and he has calculated that he will be able to save 2/5 of the remaining amount before the end of the summer. If his calculations are correct, what fraction of the cost of the new car will he still need to save at the end of summer vacation?

A. 6/36
B. 8/35
C. 12/35
D. 23/35
E. 29/35
If Andre has saved 3/7 of the cost of a new car, he has 4/7 of the cost remaining. Since he will be able to save 2/5 of the remaining cost, he will be able to save 2/5 x 4/7 = 8/35 of the total cost of the new car before the end of the summer.

Thus, he will still have 1 - (3/7 + 8/35) = 1 - (15/35 + 8/35) = 1 - 23/35 = 12/35 of the cost of the car left to save.

Answer: C

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