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A researcher investigating mosquito populations recorded a
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14 Sep 2013, 20:38
14 Sep 2013, 20:38
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A researcher investigating mosquito populations recorded a list of estimates of mosquito populations at each of \(n\) different marshland locations in a certain country. The distribution of these estimates was symmetric about the average (arithmetic mean), and 70% of these population estimates were within one standard deviation of the mean. Of these estimates, 75 were more than one standard deviation below the mean. Approximately how many of the estimates were within one standard deviation of the mean?
A) 175
B) 350
C) 375
D) 425
E) 500
A) 175
B) 350
C) 375
D) 425
E) 500
Re: A researcher investigating mosquito populations recorded a
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14 Sep 2013, 23:53
14 Sep 2013, 23:53
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carcass wrote:
A researcher investigating mosquito populations recorded a list of estimates of mosquito populations at each of \(n\) different marshland locations in a certain country. The distribution of these estimates was symmetric about the average (arithmetic mean), and 70% of these population estimates were within one standard deviation of the mean. Of these estimates, 75 were more than one standard deviation below the mean. Approximately how many of the estimates were within one standard deviation of the mean?
A) 175
B) 350
C) 375
D) 425
E) 500
A) 175
B) 350
C) 375
D) 425
E) 500
If 70% of population is within 1 standard deviation mean then 30% are more than 1 standard deviation below the mean.
Taking symmetric about the mean,
75 are more than 1 sd below the mean therefore these 75 constitute 15% (Taking 15% below the mean and 15% above the mean)
Therefore total population is 500.
Therefore 70% of 500 is 350. who are within 1 standard deviation from the mean.
Hence B
General Discussion
Re: A researcher investigating mosquito populations recorded a
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15 Sep 2013, 03:17
15 Sep 2013, 03:17
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Expert Reply
shameekv wrote:
carcass wrote:
A researcher investigating mosquito populations recorded a list of estimates of mosquito populations at each of \(n\) different marshland locations in a certain country. The distribution of these estimates was symmetric about the average (arithmetic mean), and 70% of these population estimates were within one standard deviation of the mean. Of these estimates, 75 were more than one standard deviation below the mean. Approximately how many of the estimates were within one standard deviation of the mean?
A) 175
B) 350
C) 375
D) 425
E) 500
A) 175
B) 350
C) 375
D) 425
E) 500
If 70% of population is within 1 standard deviation mean then 30% are more than 1 standard deviation below the mean.
Taking symmetric about the mean,
75 are more than 1 sd below the mean therefore these 75 constitute 15% (Taking 15% below the mean and 15% above the mean)
Therefore total population is 500.
Therefore 70% of 500 is 350. who are within 1 standard deviation from the mean.
Hence B
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Hope it helps.
