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

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CEO
Joined: 21 Jan 2007
Posts: 2760
Location: New York City
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Mike has to take 5 tests containing 80 questions each. After [#permalink]  03 Nov 2007, 15:24
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
Posts: 85
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Kudos [?]: 0 [0], given: 0

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
Senior Manager
Joined: 04 Jun 2007
Posts: 374
Followers: 1

Kudos [?]: 22 [0], given: 0

Re: Easy Avg question [#permalink]  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
Director
Joined: 11 Jun 2007
Posts: 932
Followers: 1

Kudos [?]: 80 [0], given: 0

Re: Easy Avg question [#permalink]  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
CEO
Joined: 29 Mar 2007
Posts: 2585
Followers: 17

Kudos [?]: 245 [0], given: 0

Re: Easy Avg question [#permalink]  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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