in a study reported in the Flurry Blog on Oct. 29, 2012, the mean age of tablet users was 34 yrs, with a standard deviation of 15 years. Assuming a normal distribution, what is the approximate probability of picking a random sample of 40 tablet users with a mean age between 31 and 35 yrs?
.56, between z = +1.27 and -0.42 |
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.56, between z = 31 and 35 |
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.56, between z = -1.27 and +0.42 |
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.56 between z = -2.27 and +0.42 |
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none of the above |
Given that the mean age of tablet users was
= 34 yrs, with a standard deviation of
= 15 years. Assuming a normal distribution the probability of mean
age between
= 31 and
= 35 years is calculated by finding the Z score at 31 and 35
as:
and at Mean = 35
Thus the probability P(31<<35)
= P(-1.27 < Z < 0.42) the probability of a normal
distribution can be calculated using the excel formula for normal
distribution which is
=NORM.S.DIST(0.42,TRUE)-NORM.S.DIST(-1.27,TRUE), thus the
probability is computed as 0.56.
So, the correct answer would be:
0.56, between z = -1.27 and +0.42
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