What is the sum of all the 2 digit numbers of 100?

Answer 1

We're not quite sure what the "2 digit numbers of 100" are.

Do you mean all the "2-digit numbers you say as you count to 100" ?

If that's it, then here's how to sum them:

There are 100 of them, minus (1 through 9, and 100) = 100 - 10 numbers = 90 numbers.

Make pairs of them . . .

10 + 99 = 109

11 + 98 = 109

12 + 97 = 109

13 + 96 = 109

14 + 95 = 109

.

.

etc.

There are 45 pairs, and every pair adds to 109.

So the sum of all 90 numbers is (45 x 109) = 4,905.