All the numbers from 10 to 99 are positive 2 digit integers
18 positive integers and 36 integers (negative and positive)
There is no such thing as "intergers".The complete list of two-digit positive whole numbers lists 90 of them.
There are 21 two-digit prime numbers.
The only pair of positive single-digit numbers which give a product of 81 are 9 and 9.
There are five such numbers.
7 two-digit numbers.
90
I believe that the numbers One and Nine fit the bill as they would be 1x9= 9 and 1+9=10.
The two-digit positive integers with a tens digit of 3 are: 30 31 32 33 34 35 36 37 38 39
There are 2941 4-digit numbers such no two of its digits differ by 1.
36