Find the greatest number 23a68b, which is divisible by 3 but NOT divisible by 9.

A four digit number is formed by writing a two digit number together twice like: 15:15, -3737 etc. A number of this form will be exactly divisible by which of the following numbers 

many times will the buttons of a typewriter be pressed to write the numbers 121 to 1346?

The average of six consecutive odd numbers is 26. Find the difference between the largest and the smallest of these numbers.

Which of the following numbers is divisible by 25?

The value of (81)3.6 * (9)2.7/ (81)4.2 * (3) is __

Find the average of the cubes of the first five natural numbers. 

For which value of x the seven-digit number 8439x53 is divisible by 99?