Question

How many positive three-digit integers have the property that the tens digit is greater than or equal to the hundreds digit and the ones digit is greater than or equal to the tens digit?

Please help :)
thanks
-Zach

Answer 1

9a

Answer 2

Let a = hundreds, b = tens, c = ones

a ≤ b ≤ c

Examples of what you are seeking are:

111
112
113...

122
123
124...

133
134
135...

222
223
224...

...999

Unfortunately, I cannot think of an equation to help you solve this problem. Sorry.