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The average age of all the students of a class is 23 years. The averag

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Bunuel
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The average age of all the students of a class is 23 years. The averag [#permalink] New post   26 Jan 2021, 08:00
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The average age of all the students of a class is 23 years. The average age of boys of the class is 25 years and that of the girls is 20 years. If the number of girls in the class is 30, then find the number of boys in the class.

(A) 30
(B) 35
(C) 40
(D) 45
(E) 50
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D
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meanup
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Re: The average age of all the students of a class is 23 years. The averag [#permalink] New post   26 Jan 2021, 08:46
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Quick approach,

Ans D 45
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seekshubham
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Re: The average age of all the students of a class is 23 years. The averag [#permalink] New post   12 Apr 2021, 23:23
It can be solved using weighted Average

23={X/X+30}*25 + {30/X+30}*20

By solving it we get X=45 Ans
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Re: The average age of all the students of a class is 23 years. The averag [#permalink] New post   06 May 2021, 00:34
\(\frac{25b+600}{b+30} = 23\)

Solving, b = 45

Answer: D
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Re: The average age of all the students of a class is 23 years. The averag [#permalink] New post   14 Nov 2022, 12:40
when the average becomes 23 age of girls increase by 3 years and that of boys decreased by 2 years so
3*30=90 and the increasing age of total girls and decreasing age of total boys are equal which is 90 so,
since the average age of boys decreased by 2 years for each: 90/2 becomes the total number of boys.
prove: average = ((45*25)+(30*20))/75)=23
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Re: The average age of all the students of a class is 23 years. The averag [#permalink]
14 Nov 2022, 12:40
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