Help with Probability?

1. In New England, 75% of the houses have a garage, 12% of the houses have a backyard and 45% of the houses have a garage and a backyard. What is the probability that a house has a backyard given that it has a garage.

The possible answers are 3/5, 3/8, 5/3 and 2/7

2. In a survey, 70% of people say that they read books, 25% of people say that they watch movies and 20% of people say that they watch movies and also read books. What is the probability that a person watches movies, given that he also reads books.

The possibilities are 2/7, 4/5, 7/4, and 1/7.

3.You are asked to roll an 8-sided die. Event A is rolling a Number multiple of 2, and event B is rolling a number multiple of 4. Find P(A,B)

The possibilities are 1/1, 5/6, 1/4, 1/5

4. You are asked to roll a six-sided die. Event A is rolling an odd number, and event B is rolling a prime number. Find the probability of rolling a prime number given the number you rolled is an odd number.

The possibilities are 2/3, 7/6, 3/4 and 1/2.

1 Answer

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  • 8 years ago
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    1. The numbers that concern us here are the houses that have garages (75%) and the number that have both a backyard and garage (45%). Our ratio of houses with garages that have backyards is 45:75 or 45/75 or 3/5.

    2. 70% of people read books. 20% both read books and watch movies. Therefore our ratio of book readers who also watch movies is 20:70 or 2/7.

    3. If what you are asking here is what is the chance of throwing a number that is the intersection of A,B, then there are only 2 numbers that fit that criteria. Those would be 4 and 8. The ratio for an 8 sided die would be 2:8 or 2/8 or 1/4.

    4. The odd numbers on a die are 1,3 and 5. Of these, 2 are prime numbers (3 and 5). Therefore the ratio for rolling a prime number given that the rolled number is odd is 2:3 or 2/3.

    Source(s): Too many years teaching math.
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