# Statistics: Five Probability multiple choice questions

1. A kindergarden class consists of 14 boys and 11 girls. If the teacher selects children from the class using random sampling:

a. what is the probability that the first child selected will be a girl?

b. if the teacher selects a random sample of n=3 children and the first two children are both boys, what is the probability that the third child selected will be a girl?

2. For each of the following z-scores, sketch a normal distribution and draw a vertical line at the location of the z-score. Then determine whether the body is to the right or left of the line and find the proportion in the body.

a. z= 0.75

b. z= -1.40

c. z= 0.85

d. z= -2.10

3. the distribution of IQ scores is normal with mean= 100 and standard deviation =15

What proportion of the population has IQ scores?

a. greater than 115?

b. greater than 130?

c. greater than 145?

4. A multiple choice test has 48 questions each with four response choices. If a student is simply guessing at the answers

a. what is the probability that a student would get more than 18 answers correct simply by guessing?

5. A trick coin has been weighted so that heads occurs with a probability of p=2/3, and p(tails) = 1/3. Iif you toss this coin 72 times

a. how many heads would you expect to get on average?

b. what is the probability of getting more than 50 heads?

c. what is the probability of getting exactly 50 heads?

#### Solution Preview

See the attached files.

1. Note that there are 25 students in the class

a) The probability of getting a girl on the first pick is 11/25

b) After two boys are selected, there are 12 boys left, 11 girls and 23 students in the class. Thus the probability of getting a girl on the third pick is 11/23.

2. To calculate the normal score porportion, you will need a normal calculator here http://stattrek.com/tables/normal.aspx

a) z = 0.75, body is on the left side. Porportion of the body is 0.7734

b) z = -1.40, body is on the right side, porportion of ...

#### Solution Summary

Statistics: Five Probability multiple choice questions