LH9a
Practice - Probability
TRY TO ANSWER IN TWO AND A HALF MINUTES.
QUESTIONS
QUESTIONS
1. What is the probability that you can guess the birth month of a stranger?
2. You give lollipops to each of 12 children at the playground. You give 6 red ones, 3 blue ones, 2 green ones, and one yellow one. What is the probability that a child received a lollipop whose color was not green?
3. You choose three people from a group of eight. Five of the eight are men; three are women. What is the probability that all three of the women are chosen?
4. At a baseball park, the concession stand is open whenever the park is open. The chances that the park will be open on any day is 70%. What is the probability that the concession stand will be open during all five days, Monday through Friday?
5. A roulette wheel has eight sections. Two of the sections are blue, three are red, one is white, and two are green. If you spin the wheel one time, what is the probability of not getting red?
6. A show sells 150 adult tickets and 50 children's tickets. There is a drawing during the show, in which one ticket-holder will be given a prize. What is the probability that the winner will be a child?
7. You have the ten numbers 1 through 10. Is the probability of drawing one even number and then one odd number (greater than, equal to, or less than) the probability of drawing one odd number and then one even number?
ANSWERS
1. 1/12.
2. 2 green ones out of 12 is 2/12, or 1/6. So the probability of not green is 5/6.
3. The probability that the first pick is a woman is 3/8. The probability that the second pick is a woman is 2/7. The probability that the third pick is a woman is 1/6. The answer is the product of these three fractions, which is 1/56. You can multiply these fractions directly on the built-in calculator.
4. The probability that the concession stand will be open on any day is 0.7. The probability that it will be open on five days is (0.7) to the fifth power. The answer is .1680, rounded to 17%.
5. There are three red sections out of 8. So the probability is (8 -3)/8, or 5/8. Notice that information about the colors other than red is not relevant; all that is important is that these colors are not red.
6. There are 50 children's tickets out of a total of 200, so the chances of a children's ticket being drawn are 50/200 or 25%.
7. Five of the ten numbers are even. So the probability of drawing an even number the first time is 1/2. With one even number gone, the probability of drawing an odd number the second time is 5/9. The combined probability would be 1/2 times 5/9 = 5/18. The probabilities for the other case are exactly the same, since initially 5/10 = 1/2 of the numbers would be odd, and then 5/9 of the numbers would be even on the second draw. So the two probabilities would both be 5/18, and would be equal.