Proportions

Newport News is 40% black. What is the probability that if we randomly selected 25 potential jury members for a trial, no more than 10 would be black?

• µ_p̂=.4, σ_p̂=.25, P(p̂<10/25)=P(p̂<.4)=0.72

• µ_p̂=.4, σ_p̂=.098, P(p̂<10/25)=P(p̂<.4)=0.50

• µ_p̂=.4, σ_p̂=.098, P(p̂<10/25)=P(p̂<.4)=0.37

One of the often overlooked pre-conditions for sampling is the "10% rule." Your sample can't exceed 10% of the population, or else you significantly change the proportion of the population simply by removing your sample. Assume we are sampling from a population of 1700 (Warwick HS). Which of the following sample sizes would not violate the 10% rule? Choose all that qualify.

• 100

• 150

• 200

• 250

The Gallup Poll asked a random sample of 1785 adults whether they attended church during the past week.  Let p-hat be the proportion of people in the sample who attended church.  A newspaper report claims that 40% of all U.S. adults went to church last week.  Suppose this claim is true. 
What is the mean of the sampling distribution of p-hat?

• 0.4

• 0.44

• 0.56

• 0.6

28% of all Woodrow students believe Monday will be snow day. You take a sample of 50 students and find that 15 of them believe Monday will be a snow day. What does 50 represent?

• n

• P

• phat

• standard deviation

When sampling from a population with proportion p, the sample outcomes will vary.  Which of the following represents the standard deviation of the sampling distribution?

• p

30% of all dogs in a city are micro-chipped. In a sample of 500 dogs, what is the probability that less than 32% of dogs are micro-chipped?

• 0.2586

• 0.1587

• 0.8354

• 0.1398

• 0

According to the Center for Disease Control, 93% of children entering kindergarten in the U.S. are vaccinated. A school district has 180 incoming kindergarten children.

Which of the following is true concerning the shape of the sampling distribution?

• The sampling distribution is normal because n > 30

• The sampling distribution is not normal because nq is < 30

• The sampling distribution is normal because 93% of 180 is > 10

• The sampling distribution is normal because np and nq are both > 10

Your mail-order company advertises that it ships 90% of its orders within three working days. You select an SRS of 100 of the 5000 orders received in the past week for an audit.

What is the mean?

• 0.9

• 0.1

• 500

• 450

• 0.5

Your mail-order company advertises that it ships 90% of its orders within three working days. You select an SRS of 100 of the 5000 orders received in the past week for an audit.

What is the standard deviation?

• 0.04

• 0.004

• 0.3

• 0.03

Your mail-order company advertises that it ships 90% of its orders within three working days. You select an SRS of 100 of the 5000 orders received in the past week for an audit.

What Is the probability that more than 95% of the orders are delivered within three working days?

• 0.0228

• 0.4779

• 0.0478

• 0.9522