Complementary events

Question 1

What is a complementary event?

Answer 1

A complementary event has only two outcomes.

Probability (A) + Probability (B) = 1

Question 2

A and B are complementary. If the probability of A is 40%, what is the probability of B?

Answer 2

Probability (A) + Probability (B) = 1
40% is the same as 0.4 probability (divide by 100)
0.4 + P(B) = 1
so P(B) is 0.6 or 60%

Question 3

Which of the following are complementary events?

a. flipping a coin
b. rolling a die and getting an even or odd number
c. winning gold, silver or bronze medal
d. winning or losing a race

Answer 3

a, b and d are complementary events (only two outcomes possible)

Question 4

A and B are complementary. If the probability of A is 74%, what is the probability of B?

Answer 4

Probability (A) + Probability (B) = 1
74% is the same as 0.74 probability (divide by 100)
0.4 + P(B) = 1
so P(B) is 0.26 or 26%