Boston/Cambridge GMAT & GRE Math Tutor

The average of 8 numbers is 20. If after one number is removed, the average of the remaining 7 numbers is 16. What number was removed?

What's the second smallest integer with a units digit of 5, which is the square of an integer, and the cube of an integer?

has how many non-zero digits when written as a decimal?

How many factors does 40320 have?

What's the smallest non-prime integer that isn't a factor of 20! ?