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# One class in a school is 30 percent boys. If a second class that is ha

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Math Expert
Joined: 02 Sep 2009
Posts: 56269
One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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07 Jan 2019, 04:33
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25% (medium)

Question Stats:

70% (01:19) correct 30% (01:41) wrong based on 82 sessions

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One class in a school is 30 percent boys. If a second class that is half the size of the first is 40 percent boys, what percent of both classes are boys?

A. 20%
B. 25%
C. 28%
D. 30%
E. 100/3%

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Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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07 Jan 2019, 04:36
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Bunuel wrote:
One class in a school is 30 percent boys. If a second class that is half the size of the first is 40 percent boys, what percent of both classes are boys?

A. 20%
B. 25%
C. 28%
D. 30%
E. 100/3%

let class be 30 students = 9 boys
and other be 15 students = 6 boys
total 15/45 = 33.3% IMO E
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Manager
Joined: 16 May 2018
Posts: 83
Location: Hungary
Schools: Queen's MBA'20
Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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16 Jan 2019, 06:49
Bunuel :

why cant i do the same by assuming 100 as total number of students?

100.
Class A: 30% boys =30
Class B: 50..so 40% of 50 =20

30+20=50

50/100= 1/2
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Joined: 02 Sep 2009
Posts: 56269
Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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16 Jan 2019, 07:27
hsn81960 wrote:
Bunuel :

why cant i do the same by assuming 100 as total number of students?

100.
Class A: 30% boys =30
Class B: 50..so 40% of 50 =20

30+20=50

50/100= 1/2

If you assume that there are 100 students in A and 50 students in B, then there are 150 students in total, so the percentage of boys will be 50/150*100 = 1/3*100%.
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Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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16 Jan 2019, 10:14
Thank you so much Brunel for the quick reply
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Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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21 Jan 2019, 19:53
Bunuel wrote:
One class in a school is 30 percent boys. If a second class that is half the size of the first is 40 percent boys, what percent of both classes are boys?

A. 20%
B. 25%
C. 28%
D. 30%
E. 100/3%

We can let the number of students in the first class = 60, and thus there are 0.3 x 60 = 18 boys in the first class.

The second class then has 30 students and there are 0.4 x 30 = 12 boys in the second class.

The total number of students in both classes is 60 + 30 = 90, and the total number of boys in both classes is 18 + 12 = 30.

Thus, the percentage of boys in both classes is 30/90 x 100 = 1/3 x 100 = 100/3%.

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Re: One class in a school is 30 percent boys. If a second class that is ha  [#permalink]

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08 Feb 2019, 07:36
Bunuel wrote:
One class in a school is 30 percent boys. If a second class that is half the size of the first is 40 percent boys, what percent of both classes are boys?

A. 20%
B. 25%
C. 28%
D. 30%
E. 100/3%

Let students be 100, class A will have 30 boys

Class B => half size of A = 50, 40% of A = 20

20+30 = 50/150 * 100

100/3 %

E
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Re: One class in a school is 30 percent boys. If a second class that is ha   [#permalink] 08 Feb 2019, 07:36
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