The answer is 26/36, or as a decimal, 0.72.
Explanation:
There are 26 lowercase letters in the alphabet and 10 numbers from 0-9, making 36 different possibilities (26+10 = 36). Then, because we are finding the probability of the program choosing a letter, the probability is the number of lowercase letters out of the total number of possibilities, which is 26/36. This fraction as a decimal rounded is 0.72.