Posted by **bobby** on Wednesday, March 18, 2009 at 10:19am.

Violence in School, I An SRS of 400 American adults is asked “What do you think is the most serious problem facing our schools?” Suppose that in fact 40% of all adults would answer “violence” if asked this question. The proportion p of the sample who answers “violence” will vary in repeated sampling. In fact, we can assign probabilities to values of p using the normal density curve with mean 0.4 and standard deviation 0.023. Use the density curve to find the probabilities of the following event:

a.At least 45% of the sample believes that violence is the school’s most serious problem.

b.Less than 35% of the sample believes that violence is the most serious problem.

c.The sample proportion is between 0.35 and 0.45.

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**Sean**, Wednesday, March 18, 2009 at 4:24pm
So, you are assuming a true population with a normal distribution of 0.4; 0.023)

A)

Convert 0.45 to a Z score: (0.45 - 0.40) / 0.023 = +2.17

Look up on a z-table chart. Greater than +2.17 yields .0150 = 1.5%

B)

<= 0.35 has the exact opposite Z score: (0.35 - 0.40) / 0.023 = -2.17

Less than -2.17 yields .0150 = 1.5% (same answer as A)

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**Sean**, Wednesday, March 18, 2009 at 4:26pm
Forgot C. That's probably obvious after you have A + B:

C)

100% - 1.5% - 1.5% = 97%

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**Anonymous**, Wednesday, December 7, 2011 at 8:30pm
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