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# Last year at a particular day care center, 98% of the children were si

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Manager
Joined: 02 Jun 2015
Posts: 190
Location: Ghana
Last year at a particular day care center, 98% of the children were si  [#permalink]

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10 Feb 2017, 01:20
2
00:00

Difficulty:

65% (hard)

Question Stats:

37% (01:42) correct 63% (02:15) wrong based on 32 sessions

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Last year at a particular day care center, 98% of the children were sick less than 40 days and 50% of the children were sick less than 25 days. If days sick was normally distributed among the children, what is the standard deviation?

A) 65
B) 48
C) 24
D) 15
E) 7.5

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Retired Moderator
Joined: 28 May 2014
Posts: 528
GMAT 1: 730 Q49 V41
Re: Last year at a particular day care center, 98% of the children were si  [#permalink]

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11 Feb 2017, 01:10
1
The pattern follows the normal distribution.

50% children are sick less than 25 days = i.e. 1 SD Approx (it should be 68% if it follows normal distribution);
98% children are sick less than 40 days = i.e. 2 SD Approx (it should be 95% if it follows normal distribution);

Therefore, the difference is 40 -15 = 15% = this includes 1 SD from both side of the median (refer to the graph);
Hence, 1SD = 15/2 = 7.5 %;
Attachments

Normal-distribution-curve.jpg [ 26.46 KiB | Viewed 581 times ]

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Posts: 50000
Re: Last year at a particular day care center, 98% of the children were si  [#permalink]

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11 Feb 2017, 02:54
1
duahsolo wrote:
Last year at a particular day care center, 98% of the children were sick less than 40 days and 50% of the children were sick less than 25 days. If days sick was normally distributed among the children, what is the standard deviation?

A) 65
B) 48
C) 24
D) 15
E) 7.5

Normal distribution and its 8.2-95.4-99.7 rule are NOT tested on the GMAT.
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Re: Last year at a particular day care center, 98% of the children were si &nbs [#permalink] 11 Feb 2017, 02:54
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# Last year at a particular day care center, 98% of the children were si

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