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The average height of the boys in a class is 71 inches and t

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Carcass
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The average height of the boys in a class is 71 inches and t [#permalink] New post   10 Sep 2020, 10:43
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The average height of the boys in a class is 71 inches and the average height of the girls in the class is 62 inches. The average height for the students in the class is 65 inches.

Quantity A
Quantity B
The number of girls in the class
The number of boys in the class



A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   10 Sep 2020, 10:44
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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   13 Sep 2020, 01:50
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Let total number of boys and girls in the class be x and y

total height of boys in the class =71x

total height of girls in the class =62y

now
total height of class is = 71x+62y

but given avg of whole class =65

so 71x+62y=65(x+y)
2x=y

there are twice as many girls as boys so no of girls are greater than boys

Option A is correct

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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   30 Sep 2020, 20:26
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1 girl bring -3 difference to the mean and 1 guy adds +9 to the mean of girls
so 2 girls would constitute = -6 and 1 guy would add +9 resulting in +3 which is exactly the difference between girls height and mean
so for 2 girls there has to be 1 guy and thus answer choice A
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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   05 Oct 2020, 12:06
Let's say boys be B and girls be as G.

Avg. Weight formula
65 = [71*B + 62*G]/[B + G]

65(B + G) = 71*B + 62*G

3G = 6B
G = 2B

Doesn't this mean 1 girl is equal to 2 boys?
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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   05 Oct 2020, 14:31
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gagangm wrote:
Let's say boys be B and girls be as G.

Avg. Weight formula
65 = [71*B + 62*G]/[B + G]

65(B + G) = 71*B + 62*G

3G = 6B
G = 2B

Doesn't this mean 1 girl is equal to 2 boys?


Yes. For a total of three persons.

One female and two males
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Re: The average height of the boys in a class is 71 inches and t [#permalink] New post   06 Oct 2020, 05:31
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Carcass wrote:
gagangm wrote:
Let's say boys be B and girls be as G.

Avg. Weight formula
65 = [71*B + 62*G]/[B + G]

65(B + G) = 71*B + 62*G

3G = 6B
G = 2B

Doesn't this mean 1 girl is equal to 2 boys?


Yes. For a total of three persons.

One female and two males


This is not correct.
B = number of boys
G = number of girls

G = 2B tells us that the number of girls is equal to TWICE the number of boys.
We can also verify this by finding values of B and G that satisfy the equation G = 2B
For example, G = 10 and B = 5 satisfies the equation G = 2B (notice that the number of girls is twice the number of boys)

Another way to avoid misreading G = 2B is to rewrite it in ratio form.
Take: G = 2B
Divide both sides by B to get: G/B = 2
This is the same as: G/B = 2/1
Or we can write: G:B = 2:1
This tells us that there are two girls for every one boy (i.e., the number of girls is twice the number of boys)
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Re: The average height of the boys in a class is 71 inches and t [#permalink]
06 Oct 2020, 05:31
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