Answer:
45 numbers
Explanation:
The 10-digit numbers are from 10-99. We can manually analyze each tenth digit and see if we can find a pattern from it. First, 10-19 ~ 10 is the only number in the sequence where the tenth digit is greater than the unit digit (because 1 > 0). In every other case, 1 is less than or equal to the unit digit.
Next, 20-29 ~ 20 and 21 are the two numbers where the tenth digit is greater than the unit digit
30-39 ~ 30, 31, 32 follow the property
40-49 ~ 40, 41, 42, 43 follow the property
We can keep going, but we can see that there is a pattern. The number of numbers that correspond with the property for each set of 10 numbers is equal to the value of the tenth digit. We see that for the 40s, there are 4 numbers. For the 20s, on the other hand, there are 2 numbers. This pattern carries through:
50-59 ~ 5 numbers, 60-69 ~ 6 numbers, 70-79 ~ 7 numbers, 80-89 ~ 8 numbers, 90-99 ~ 9 numbers
We need to find how many 2-digit numbers total follow the property. We can just add our results together to get our answer:
1+2+3+4+5+6+7+8+9=45