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Chapter 5: Q. 47 (page 328)
Dogs and cats In one large city, of all households own a dog, own a cat, and own both. Suppose we randomly select a household. What鈥檚 the probability that the household owns a dog or a cat?
The likelihood that the household owns either a dog or a cat is
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The two-way table summarizes data on whether students at a certain high school eat
regularly in the school cafeteria by grade level.
a. If you choose a student at random, what is the probability that the student eats
regularly in the cafeteria and is not a grader?
b. If you choose a student at random who eats regularly in the cafeteria, what is the probability that the student is a grader?
c. Are the events 鈥�grader鈥� and 鈥渆ats regularly in the cafeteria鈥� independent?
Justify your answer.
The most common bet in craps is the 鈥減ass line.鈥� A pass line bettor wins immediately if either a or ancomes up on the first roll. This is called a natural. What is the probability that a natural does not occur?
a.
b.
c.
d.
e.
Smartphone addiction? A media report claims that of U.S. teens with smartphones feel addicted to their devices. A skeptical researcher believes that this figure is too high. She decides to test the claim by taking a random sample of U.S. teens who have smartphones. Only of the teens in the sample feel addicted to their devices. Does this result give convincing evidence that the media report鈥檚 claim is too high? To find out, we want to perform a simulation to estimate the probability of getting or fewer teens who feel addicted to their devices in a random sample of size from a very large population of teens with smartphones in which 50% feel addicted to their devices.
Let = feels addicted and = doesn鈥檛 feel addicted. Use a random number generator to produce random integers from to . Record the number of 鈥檚 in the simulated random sample. Repeat this process many, many times. Find the percent of trials on which the number of 鈥檚 was or less.
BMI (2.2, 5.2, 5.3) Your body mass index (BMI) is your weight in kilograms divided by
the square of your height in meters. Online BMI calculators allow you to enter weight in
pounds and height in inches. High BMI is a common but controversial indicator of being
overweight or obese. A study by the National Center for Health Statistics found that the
BMI of American young women (ages 20 to 29) is approximately Normally distributed
with mean 26.8 and standard deviation 7.4.
27
a. People with BMI less than 18.5 are often classed as 鈥渦nderweight.鈥� What percent of
young women are underweight by this criterion?
b. Suppose we select two American young women in this age group at random. Find the
probability that at least one of them is classified as underweight.
Lucky penny? Harris Interactive reported that of U.S. adults believe that
finding and picking up a penny is good luck. Assuming that responses from different
individuals are independent, what is the probability of randomly selecting U.S. adults
and finding at least person who believes that finding and picking up a penny is good
luck?
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