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# Average of 75 students is 82, out of which average of 42 students is 7

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Math Expert
Joined: 02 Sep 2009
Posts: 58464
Average of 75 students is 82, out of which average of 42 students is 7  [#permalink]

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20 Feb 2019, 05:20
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Difficulty:

55% (hard)

Question Stats:

60% (02:34) correct 40% (02:21) wrong based on 45 sessions

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Average of 75 students is 82, out of which average of 42 students is 79. What is the average of the remaining 33 students rounded to the nearest integer?

A. 84
B. 85
C. 86
D. 87
E. 88

The average marks of 75 students is 82, out of which the average of 42 students is 79. What is the average of the remaining 33 students?

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Re: Average of 75 students is 82, out of which average of 42 students is 7  [#permalink]

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20 Feb 2019, 08:55
1
Bunuel wrote:
Average of 75 students is 82, out of which average of 42 students is 79. What is the average of the remaining 33 students rounded to the nearest integer?

A. 84
B. 85
C. 86
D. 87
E. 88

The average marks of 75 students is 82, out of which the average of 42 students is 79. What is the average of the remaining 33 students?

sum for 75 students ; 75*82 = 6150
sum of 42 students ; 42 * 79 = 3138
so for 33 students sum = 6150-3138 ; 2832
avg ; 2832/33; 85.8 ~ 86 IMO C
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Re: Average of 75 students is 82, out of which average of 42 students is 7  [#permalink]

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20 Feb 2019, 09:28
1
Bunuel wrote:
Average of 75 students is 82, out of which average of 42 students is 79. What is the average of the remaining 33 students rounded to the nearest integer?

A. 84
B. 85
C. 86
D. 87
E. 88

The average marks of 75 students is 82, out of which the average of 42 students is 79. What is the average of the remaining 33 students?

All 75 students have an average of 82

but 42 students have an average of 79.
Therefore these 42 students are of the average by 3 points each and this difference has to be adjusted to the remaining 33 students.
Hence 42*3 = 126

These 126 points will be adjusted to the average of the remaining 33 students
=> 126/33 = 3.81 = approx 4

Now the average for the 33 students = 82 + 4 = 86.

Hence the correct answer is 86.
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Re: Average of 75 students is 82, out of which average of 42 students is 7  [#permalink]

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22 Feb 2019, 16:43
Bunuel wrote:
Average of 75 students is 82, out of which average of 42 students is 79. What is the average of the remaining 33 students rounded to the nearest integer?

A. 84
B. 85
C. 86
D. 87
E. 88

The sum of the 75 students is 75 x 82 = 6,150.

The sum of the 42 students is 42 x 79 = 3,318.

Thus, the sum of the remaining 33 students is 6,150 - 3,3318 = 2,832, and their average is 2,832/33 = 85.8, rounded to 86.

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Re: Average of 75 students is 82, out of which average of 42 students is 7   [#permalink] 22 Feb 2019, 16:43
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