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?

 

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 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

Which of the following are disjoint/mutually exclusive?

• having brown hair and having brown eyes

• Getting an A in Statistics and getting a B in Chemistry

• Getting an A in Statistics and getting a B in Statistics

• Having brown hair and having blue eyes

Answer explanation

Events are disjoint/mutually exclusive if they cannot BOTH happen. You can't get both an A and a B in Statistics

Which of the following events are independent?

• Drawing a King from a deck of cards and rolling a 5 on a die

• Having a high GPA and getting a college scholarship for academics

• The age of a driver and their likelihood of being in a car accident

• Having brown hair and brown eyes

Answer explanation

Independent means there is no relationship between the two events - they do not affect each other.

A survey shows that 50% of adults in America approve of the president's recent policy statements. You select three adults at random. What is the probability that they all approve of the statements?

Answer explanation

ALL means the first AND the second AND the third approve of the statements. AND means multiply.

Ms. Timlin collected data from her students and found that 45% have brown eyes, 20% have blue eyes, and the rest have other colored eyes. If you select a student at random, what is the probability that they have brown or blue eyes?

If A and B are independent, then you can ___ their probabilities to find the probability of A ___ B

• multiply, and

• add, and

• multiply, or

• add, or

If A and B are mutually exclusive, then you can ___ their probabilities to find the probability of A ___ B

• multiply, and

• add, and

• multiply, or

• add, or