The sum of two numbers is 528 and their HCF is 33. How many such pairs exist?

Find the greatest number that will divide 398, 436, and 542 leaving remainders 7, 11, and 15 respectively.

The LCM of two numbers is 2400. Which of the following cannot be their HCF?

What is the least number which when divided by 6, 9, 12, 15, and 18 leaves remainder 2 in each case?