What is the probability that a two-digit number selected at random has a tens digit less than its units digit? Express your answer as a common fraction.
There are: 99 - 10 + 1 =90 2-digit numbers between 10 and 99.
There are: 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 =36 numbers whose tens digit is LESS than its units digit.
36 / 90 =40% probability