Chapter 5: Q. T5.8 (page 357)
In a class, there are girls and boys. If the teacher selects two students at random
to attend a party with the principal, what is the probability that the two students are the
same sex?
The correct option is:
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Crawl before you walk (At what age do babies learn to crawl? Does it take
longer to learn in the winter, when babies are often bundled in clothes that restrict their
movement? Perhaps there might even be an association between babies’ crawling age and
the average temperature during the month they first try to crawl (around months after
birth). Data were collected from parents who brought their babies to the University of
Denver Infant Study Center to participate in one of a number of studies. Parents reported
the birth month and the age at which their child was first able to creep or crawl a distance
of feet within one minute. Information was obtained on infants. Crawling age is given in weeks, and average temperature (in degrees Fahrenheit) is
given for the month that is months after the birth month.
a. Make an appropriate graph to display the relationship between average temperature and
average crawling age. Describe what you see.
Some computer output from a least-squares regression analysis of the data is shown.
b. What is the equation of the least-squares regression line that describes the relationship
between average temperature and average crawling age? Define any variables that you
use.
c. Interpret the slope of the regression line.
d. Can we conclude that warmer temperatures months after babies are born causes them
to crawl sooner? Justify your answer.
Grandkids Mr. Starnes and his wife have grandchildren: Connor, Declan, Lucas, Piper, Sedona, and Zayne. They have extra tickets to a holiday show, and will randomly select which grandkids get to see the show with them.
a. Give a probability model for this chance process.
b. Find the probability that at least one of the two girls (Piper and Sedona) get to go to the show.
Body image A random sample of U.S. college students was asked, “What is your perception of your own body? Do you feel that you are overweight, underweight, or about right?” The two-way table below summarizes the data on perceived body image by gender.
Suppose we randomly select one of the survey respondents.
a. Given that the person perceived his or her body image as about right, what’s the
probability that the person is female?
b. If the person selected is female, what’s the probability that she did not perceive her body image as overweight?
Languages in Canada Canada has two official languages, English and French. Choose a Canadian at random and ask, “What is your mother tongue?” Here is the distribution of responses, combining many separate languages from the broad Asia/Pacific region
a. Explain why this is a valid probability model.
b. What is the probability that the chosen person’s mother tongue is not English?
c. What is the probability that the chosen person’s mother tongue is one of Canada’s official languages?
What kind of vehicle? : Randomly select a new vehicle sold in the United States in a certain month. The probability distribution for the type of vehicle chosen is given here.
| Vehicle Type | Passenger car | Pickup Truck | SUV | Crossover | Minivan |
| Probability | |
a. What is the probability that the vehicle is a crossover? How do you know?
b. Find the probability that vehicle is not an SUV or Minivan .
c. Given that the vehicle is not a passenger car, what is the probability that it is a pickup truck?
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