7.5 Team Challenge (C)

In a study done on the life expectancy of 500 people in a certain geographic region, the mean age at death was 72 years and the standard deviation was 5.3 years. If a sample of 50 people from this region is selected, find the probability that the mean life expectancy will be less 70 years.

• 0.8303

• -2.67

• 0.8300

• 0.0038

The scores of students on the ACT college entrance exam in a recent year were normally distributed with a mean of 18.6 and a standard deviation of 5.9. If a random sample of 100 students is taken, what is the probability that the mean of the sample is greater than 20?

• 0.9911

• 0.0089

• 0.8901

• 2.37

The weights of adult males are normally distributed with a mean of 172 pounds and a standard deviation of 29 pounds. What is the probability that 25 randomly selected adult males will have a mean weight between 180 and 190 pounds?

• 0.9162

• 0.0828

• 0.9990

• 1.38

Engineers must consider the breadths of male heads when designing motorcycle helmets. Men have head breadths that are normally distributed with a mean of 6.0 inches and a standard deviation of 1.0 inch. If one male is randomly selected, find the probability that his head breadth is more than 6.2 inches.

• 0.5793

• 0.2000

• 0.4720

• 0.4207