How many 3-digit numbers have the property that the units digit is at least twice the tens digit plus 5?
Possible 10's digit Units digit
0 5, 6,7,8,9
1 7, 8, 9
2 9
We have 9 possibilities for the hundreds digit in each case.....so....
9 ( 5 + 3 + 1) =
9 (9) =
81 such three-digit numbers
