A parking lot has sixty-eight parking spaces numbered from 1 to 68. There are no cars in the parking

A parking lot has sixty-eight parking spaces numbered from 1 to 68. There are no cars in the parking lot when Jillian pulls in and randomly parks. What is the probability that the number on the parking space where she parks is greater than or equal to 21?

We want P(X>=21). This is also found by taking 1 - P(X <= 20).

P(X<=20) = 20/68. Reduced using a GCF of 4, we get 5/17.

P(X >=21) = 1 - 5/17 = 12/17