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# Mike has to take 5 tests containing 80 questions each. After

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CEO
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Mike has to take 5 tests containing 80 questions each. After [#permalink]

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03 Nov 2007, 15:24
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Mike has to take 5 tests containing 80 questions each. After completing four tests, Mike has an average of 80 percent of correct answers. What is the least number of questions Mike needs to get right in the ffth test to bring his average to 82%?

70
72
75
78
80
Current Student
Joined: 03 Oct 2006
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03 Nov 2007, 15:31
B 72

I'm sure there's a simple equation, but I did this piece meal.

80% of 80 = 64
64 * 4 = 256 correct answers on 4 tests

82% of (80 * 5) = 328

328-256 = 72
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03 Nov 2007, 15:33
bmwhype2 wrote:
Mike has to take 5 tests containing 80 questions each. After completing four tests, Mike has an average of 80 percent of correct answers. What is the least number of questions Mike needs to get right in the ffth test to bring his average to 82%?

70
72
75
78
80

320*80%= 256 right
400*82%= 328 right
he needs to get another 328-256= 72 questions right
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03 Nov 2007, 15:37
bmwhype2 wrote:
Mike has to take 5 tests containing 80 questions each. After completing four tests, Mike has an average of 80 percent of correct answers. What is the least number of questions Mike needs to get right in the ffth test to bring his average to 82%?

70
72
75
78
80

another approach:

80% * 4 = 320
82% * 5 = 410
so we know he as to get 90% on his 5th test

.9*80 = 72
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03 Nov 2007, 19:20
bmwhype2 wrote:
Mike has to take 5 tests containing 80 questions each. After completing four tests, Mike has an average of 80 percent of correct answers. What is the least number of questions Mike needs to get right in the ffth test to bring his average to 82%?

70
72
75
78
80

.8(320)/320=.8

256+X/400=.82

328=X+256
x=72

B
Re: Easy Avg question   [#permalink] 03 Nov 2007, 19:20
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