How many positive factors does 840 have?

If N=3¹⁰+3¹¹+3¹²+3¹³, how many positive factors does N have?

Seven times a two-digit positive number is equal to four times the number obtained by reversing the order of the digits. How many such two-digit numbers are there?

What is the median of all possible factors of 120 ?

How many times the digit 9 occurs in the numbers from 100 to 999?

How many three-digit numbers are divisible by 5?