Question

There are 900 3-digit integers, the integers between 100 and 999, inclusive. What percent of these integers contain only odd digits

Answer 1

Each digit can be one of {1, 3, 5, 7, 9}, so there are 5 choices for each. Then there are 5•5•5 = 5³ = 125 integers containing only odd digits, which means they make of 125/900 ≈ 14% of them.