Statistics Probability Rules

A consumer organization estimates that over a 1 year period, 17% of cars will need to be repaired at least once. What is the probability that two cars chosen at random will both need to be repaired? 

• 0.17x0.17

• 0.17+0.17

• 1-0.17

• 0.17

Answer explanation

BOTH means the first car AND the second car both need repairs. AND means multiply!

Suppose in a lab 24% of the mice are albino, 56% are brown, and the rest are grey. You choose one mouse at random. What is the probability that it is grey?

(a)  

 

Suppose in a lab 24% of the mice are albino, 56% are brown, and the rest are grey. You choose one mouse at random. What is the probability that it is not brown?

(a)  

A survey of 100 students found that 68% like Taco Bell. You randomly select 2 students. What is the probability that neither of them likes Taco Bell?

• 0.68 x 0.68

• 0.68 x 0.32

• 0.32 x 0.32

• 0.32 + 0.32

Answer explanation

NEITHER means the first does NOT like Taco Bell AND the second does NOT like Taco Bell

Are getting a head and getting a tail when flipping a coin mutually exclusive events?

• No

• Yes

A jar contains 4 white chips, 5 purple chips, and 1 black chip. Chips are selected randomly one at a time, and are not replaced. 
What is P(purple then black)?

• 1/18

• 2/5

• 3/7

• 4/9

John has seven keys on a ring. He gives these keys to his friend Robin and asks her to unlock a door. If two of the seven keys can unlock the door, what is the probability that Robin unlocks the door on exactly her third attempt?

There are 9 movies showing at a theater. Two are action movies, two are children’s movies, and the other movies are comedies. Ashley randomly selects 2 different movies to see, without replacement. What is the probability that the first movie is an action movie and the second movie is a comedy?