If we exclude zero from the set of integers. then is it closed under division ?

the set of integers are denoted by

Take atleast five pairs of integers and check whether they are closed under division.

If two numbers a and b are chosen from the set of integers 1 to 39 then the prodability that those numbers satisfy the equation 7a-9b=0 is

Find the sum of integers from 1 to 100 which are divisible by 2 or 3.

Find the sum of integers which are divisible by 5 from 1 to 100.

Find the sum of Integers from 1 to 100 which are divisible by 2 or 5.

Find the sum of integers which are divisible by 5 from 50 to 85.