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students in a class

by Vincelauret » Sun Mar 15, 2015 4:21 am
Hello could someone help me to solve this mats problem?

there are 42 students in a class. if there are 40% as many girls as boys, how many boys are there in the class?
a.12
b.17
c.20
d.25
e.30

Thanks for your help
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Source: — Data Sufficiency |
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by MartyMurray » Sun Mar 15, 2015 4:29 am
Vincelauret wrote:Hello could someone help me to solve this mats problem?

there are 42 students in a class. if there are 40% as many girls as boys, how many boys are there in the class?
a.12
b.17
c.20
d.25
e.30
If there are 40% as many girls(G) as there are boys(B), then G = .4B.

So the total of boys and girls = B + .4B = 42.

Combine the terms on the left side to get 1.4B = 42.

Then B = 42/1.4 = 30.

Choose e.
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by Vincelauret » Sun Mar 15, 2015 5:41 am
Thank you !!
now regarding to your solution I understand that I mistranslated the sentence in my own language....

I have to work harder!!!
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by GMATGuruNY » Sun Mar 15, 2015 6:34 am
Vincelauret wrote:Hello could someone help me to solve this mats problem?

there are 42 students in a class. if there are 40% as many girls as boys, how many boys are there in the class?
a.12
b.17
c.20
d.25
e.30
Alternate approach:

There are 40% as many girls as boys.
Thus:
G:B = 40:100 = 2:5.
Implication:
Of every 7 students, 2 are girls and 5 are boys, with the result that boys constitute 5/7 of the total number of students:
(5/7)(42) = 30.

The correct answer is E.
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by Brent@GMATPrepNow » Sun Mar 15, 2015 1:01 pm
Vincelauret wrote: there are 42 students in a class. if there are 40% as many girls as boys, how many boys are there in the class?
a.12
b.17
c.20
d.25
e.30
If you're not sure how to approach a question, you can always test the answers.

ALSO, we can eliminate answers that do not yield an integer value for the number of girls.
Take answer choice A for example.

Answer choice A) 12
If there are 12 boys, then the number of girls = 40% of 12
In other words, there are 4.8 girls.
This makes no sense, so ELIMINATE A.

We can eliminate B for the same reason.


Answer choice C) 20
If there are 20 boys, then the number of girls = 40% of 20
So, there are 8 girls
This means the TOTAL number of students = 20 + 8 = 28
HOWEVER, the question tells us that there are 42 students.
ELIMINATE C.
.
.
.

Answer choice E) 30
If there are 30 boys, then the number of girls = 40% of 30
So, there are 12 girls
This means the TOTAL number of students = 30 + 12 = 42
PERFECT! The question tells us that there are 42 students.
So, the correct answer must be E


Cheers,
Brent
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