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# M70-37

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Math Expert
Joined: 02 Sep 2009
Posts: 56307

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04 Sep 2018, 02:36
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Difficulty:

35% (medium)

Question Stats:

40% (01:33) correct 60% (02:02) wrong based on 10 sessions

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In Woodbridge Elementary school, 27% of the students are redheaded. If there are twice as many boys as there are girls, what percentage of boys are redheaded?

(1) 29% of the girls are redheaded.

(2) The school has 600 students.

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Math Expert
Joined: 02 Sep 2009
Posts: 56307

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04 Sep 2018, 02:36
Official Solution:

We’ll go for LOGICAL because that is our first choice in Data Sufficiency.

In questions with equations and variables, we must check how much information we have and how much we are missing. (1) Knowing two percentages out of three (total number of redheads & redheaded girls) and the ratio between the totals out of which those percentages are taken is enough to find the third percentage. Sufficient! (B), (C) & (E) are eliminated. (2) With the total number of students we can find the number of boys, the number of girls, and the total number of redheaded students, but without any information on the composition of hair color in each gender, we cannot tell how many redheaded boys there are. (D) is eliminated.

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Intern
Joined: 08 Dec 2017
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12 Dec 2018, 09:53
can some explain me in equations ?
Intern
Joined: 16 Oct 2018
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19 Jan 2019, 11:54
But the total no of red hair can only be found by the total no of students.
Manager
Joined: 17 Mar 2018
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14 Jun 2019, 11:27
number of boys= twice of girls
27% of total number of students are Redheads.
need to find % of redhead boys.

statement 1 states 29% of girls are redheads.

let x be % of redhead boys.

xb+.29g=.27(b+g)
we know b=2g
x2g+.29g=.27(2g+g)
x2g+.29g= .27(3g)
x2g=.81g-.29g
x2g=.52g
x= .52g/2g
x=.26 or 26%

Statement 2: 600 students.
b= 400 g= 200
27% of 600= 162.
no info on how 162 is split between boys and girls.
Re: M70-37   [#permalink] 14 Jun 2019, 11:27
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# M70-37

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