Math

2. Remember that OR=addition, so we have 6/20+2/20=8/20 or 2/5.

1.Cathy rolls a number cube that is labeled from 1 to 6. What is the probability that she rolls an even number or a multiple of 3?

P (even or multiple of 3)  = P(even) + P(multiple of 3) - P(even and multiple of 3)  =

                                             3/6      +       2/6       -     1/6  =

                                                            4/6   =     2/3

2.Joseph has 20 coins in his pocket. He has 5 nickels, 6 quarters, 7 dimes, and 2 pennies. Joseph chooses a coin at random.

What is the probability that he selects a quarter or a penny from his pocket?

P ( Q or P )  = P(Q)  + P(P)  -  P (Q and P)  =

                        6/20    +  2/20  -   0/20     =   8/20    =   2/5

3.There are 20 cards labeled from 1 to 20 in a bag. A card is randomly selected from the bag.

What is the probability of getting an even number or a 1?

P (E or 1)  =  P(E)  + P(1)  - P( E and 1)  =

                      10/20 + 1/20  - 0/20    =     11/20

All problems can be handy by learning the Principle of Inclusion-Exclusion formula. Look at CPhill's solution for more detail!