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Statistics - Standard Error and Mean

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The mean time to perform a certain task in Kindergarten follows a mound shaped
distribution. The mean time is 10 minutes with a standard deviation of 1 minute. The teachers want to establish a time such that approximately only 2.5% will take longer than this time.
A. The time is 8 minutes.
B. The time is 9 minutes.
C. The time is 11 minutes.
D. The time is 12 minutes.

In recent years, the use of the telephone as a data collection instrument for opinion polls has been steadily increasing. However, one of the major factors affecting the extent to which the telephone can be used is the refusal rate that is, the percentage of eligible subjects actually contacted who refuse to take part in the poll. Suppose that past records indicate a refusal rate of 20% in a large city. What is the probability that out of 15 people:
Answer each part using the statistical calculator or a table.
a. No one refuses to take part in the poll?

b. Exactly 2 refuse to take part in the poll?

c. At most three refuse to take part in the poll?

d. What is the mean and standard deviation of those who refuse to take part in the poll?

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(1) The area under the standard normal curve is 2.5%, that is 0.025 for z = 1.96

The time to be established = Mean + 1.96 * Standard Deviation = 10 + ...

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