Ben chooses a random integer between 1 and 50, inclusive, twice (and he may choose the same integer twice). What is the probability that at least one of the numbers Ben chooses is a multiple of $5$?
Prob that the first one is a multiple of 5 is 1/10 = 0.1
prob that the second one is a multiple of 5 is 1/10 = 0.1
probability that they are both a multiple of 5 is 1/100 = 0.01
Prob that at least one is a multiple of 5 is 0.1+0.1-0.01 = 0.19