Missing Perce

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Missing Perce

by oquiella » Wed Oct 28, 2015 5:55 pm
42. In a class, 30% of the students are girls and 70% of these girls are intelligent. What
is the percentage of boys who are intelligent?
(1) 42% of the class is intelligent.
(2) The number of girls who are intelligent is the same as the number of boys who
are intelligent.

A:D

What is the quickest approach? using 100?
Source: — Data Sufficiency |

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by theCEO » Wed Oct 28, 2015 10:58 pm
oquiella wrote:42. In a class, 30% of the students are girls and 70% of these girls are intelligent. What
is the percentage of boys who are intelligent?
(1) 42% of the class is intelligent.
(2) The number of girls who are intelligent is the same as the number of boys who
are intelligent.

A:D

What is the quickest approach? using 100?
s=students, g=girls, ig=intelligent girls, ib=intelligent boys

g = 0.3s
ig = 0.3s x 0.7 = 0.21s

(1) 42% of the class is intelligent.
ig + ib = 0.42s
0.21s + ib = 0.42s -> ib = 0.42s - 0.21s = 0.21s
ib = 21% of students-> statement sufficent

(2) The number of girls who are intelligent is the same as the number of boys who
are intelligent
ig = 0.3s x 0.7 = 0.21s
therefore ib = 0.21s
ib = 21% of students-> statement sufficent

ans = d

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by GMATGuruNY » Thu Oct 29, 2015 3:14 am
I believe that the following represents the intent of the problem:
oquiella wrote:42. In a class, 30% of the students are girls, and 70% of these girls are intelligent. What percentage of the boys in the class are intelligent?

(1) 42% of the class is intelligent.
(2) The number of girls who are intelligent is the same as the number of boys who
are intelligent.
Let the total number of students = 100.
Thus:
Total girls = 30% of 100 = 30, implying that total boys = 100-30 = 70.
Intelligent girls = 70% of 30 = 21.

Statement 1:
Total intelligent = 42% of 100 = 42.
Intelligent boys = (total intelligent) - (intelligent girls) = 42-21 = 21.
Of the 70 boys, the percentage who are intelligent = (intelligent boys)/(total boys) * 100 = 21/70 * 100 = 30%.
SUFFICIENT.

Statement 2:
Intelligent boys = intelligent girls = 21.
Of the 70 boys, the percentage who are intelligent = (intelligent boys)/(total boys) * 100 = 21/70 * 100 = 30%.
SUFFICIENT.
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