Answer:
There is 45 different 2-digit numbers.
Explanation:
My way is kinda dumb, but it still works. So, 2 digit numbers is from 10-99. We can start from the 10-19 first.
10, 11,12,13,14,15,16,17,18,19
We need to find the numbers that the tenth digit is greater than the units digit.
10, 11,12,13,14,15,16,17,18,19
Since 1 is the tenth digit, all the ones digits are all going to be bigger. Same goes with 20-29. Then you will have 2 numbers that the tenth digit is greater. My way applies when the tenth digit is only less than the ones digit, not greater. If you do this way...
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10-19: 1 number
20-29: 2 numbers
30-39: 3 numbers
40-49: 4 numbers
50-59: 5 numbers
60-69: 6 numbers
70-79: 7 numbers
80-89: 8 numbers
90-99: 9 numbers
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So, if you add 1+2+3+4+....+9(which all of you probably memorized by now) it would be 45. The answer is 45. Hope this helped!