An integer x, with 10 <= x <= 99, is to be chosen. If all choices are equally likely, what is the probability that at least one digit of x is a 7?
We have 99 - 10 + 1 = 90 possible integers
The ones that contain at least one "7" are
17, 27, 37, 47, 57, 67, 70 - 79, 87, 97 = 18 integers
So....the probability of selecting an integer with one with at least one "7" is
18 / 90 =
1/5