There are 21 two-digit prime numbers.
There are five such numbers.
7 two-digit numbers.
There are 2941 4-digit numbers such no two of its digits differ by 1.
36
There are 45 of them.
3
There are 90 two-digit numbers... starting with 10 and ending with 99.
90
All of the odd numbers between 11 and 99 inclusive are two digit numbers that are not multiples of 2. There are 45 of them.
72. (with the range of two digit numbers being from 10 to 99).
16000