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# A boy receives grades of 91, 88, 86, and 78 in four of his major subj

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Math Expert
Joined: 02 Sep 2009
Posts: 52161
A boy receives grades of 91, 88, 86, and 78 in four of his major subj  [#permalink]

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08 Feb 2018, 04:42
00:00

Difficulty:

15% (low)

Question Stats:

87% (01:08) correct 13% (01:32) wrong based on 33 sessions

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A boy receives grades of 91, 88, 86, and 78 in four of his major subjects. What must he receive in his fifth major subject in order to average 85?

(A) 86

(B) 85

(C) 84

(D) 83

(E) 82

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Joined: 26 Sep 2017
Posts: 97
Re: A boy receives grades of 91, 88, 86, and 78 in four of his major subj  [#permalink]

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08 Feb 2018, 07:33
Bunuel wrote:
A boy receives grades of 91, 88, 86, and 78 in four of his major subjects. What must he receive in his fifth major subject in order to average 85?

(A) 86

(B) 85

(C) 84

(D) 83

(E) 82

(91+88+86+78+x)/5 = 85

Solving for x we get x = 82

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Posts: 2331
A boy receives grades of 91, 88, 86, and 78 in four of his major subj  [#permalink]

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08 Feb 2018, 09:28
Bunuel wrote:
A boy receives grades of 91, 88, 86, and 78 in four of his major subjects. What must he receive in his fifth major subject in order to average 85?

(A) 86

(B) 85

(C) 84

(D) 83

(E) 82

A*n=S

First n = 4 scores, SUM:
78 + 86 + 88+ 91 = 343

Average for n = 5 (WITH the fifth score needs to be 85
A * n = S
SUM: 85 * 5 = 425

The difference in sums is the fifth score he needs
425 - 343 = 82

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Re: A boy receives grades of 91, 88, 86, and 78 in four of his major subj  [#permalink]

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08 Feb 2018, 10:02
Bunuel wrote:
A boy receives grades of 91, 88, 86, and 78 in four of his major subjects. What must he receive in his fifth major subject in order to average 85?

(A) 86

(B) 85

(C) 84

(D) 83

(E) 82

$$85*5 = 91 + 86 + 88 + 78 + n$$

Or, $$425 = 343 + n$$

Or, $$n = 82$$ Answer must be (E)
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Re: A boy receives grades of 91, 88, 86, and 78 in four of his major subj  [#permalink]

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08 Feb 2018, 20:58
91 + 88 + 86 +78 = 343

Expected average of 5 scores = 85 = 425/5. To reach the overall score 425 , the fifth score should be 82.
343 + n = 425
n = 425 - 343 = 82

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Re: A boy receives grades of 91, 88, 86, and 78 in four of his major subj &nbs [#permalink] 08 Feb 2018, 20:58
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