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A student has an average (arithmetic mean) score of 72 on his first 3

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A student has an average (arithmetic mean) score of 72 on his first 3 [#permalink]

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New post 20 Dec 2017, 02:54
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A student has an average (arithmetic mean) score of 72 on his first 3 tests. Which of the following is the least average score needed on his next two tests to bring his overall average to at least an 80?

A. 89
B. 90
C. 91
D. 92
E. 104
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Re: A student has an average (arithmetic mean) score of 72 on his first 3 [#permalink]

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New post 20 Dec 2017, 05:32
Imo D

Weighted averages
(72*3 + 2x)/ 7 >=80

X>=92

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Re: A student has an average (arithmetic mean) score of 72 on his first 3 [#permalink]

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New post 20 Dec 2017, 05:43
Bunuel wrote:
A student has an average (arithmetic mean) score of 72 on his first 3 tests. Which of the following is the least average score needed on his next two tests to bring his overall average to at least an 80?

A. 89
B. 90
C. 91
D. 92
E. 104


Use our standard weighted averages formula:
3/2 = (x - 80)/(80 - 72)
x = 92

Answer (D)
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A student has an average (arithmetic mean) score of 72 on his first 3 [#permalink]

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New post 20 Dec 2017, 09:38
Bunuel wrote:
A student has an average (arithmetic mean) score of 72 on his first 3 tests. Which of the following is the least average score needed on his next two tests to bring his overall average to at least an 80?

A. 89
B. 90
C. 91
D. 92
E. 104


Try Plug In answer choices

Start with centre (C) = 91

Total score = (72 x 3 + 91 x 2)/5 = 398/5 = 79.6 < 80 Eliminate

Now, we know that we need a slightly greater number than 91

Try (D) = 92

Total score = (72 x 3 + 92 x 2)/5 = 400/5 = 80 = 80

Answer (D) = 92
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A student has an average (arithmetic mean) score of 72 on his first 3   [#permalink] 20 Dec 2017, 09:38
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