Multiplication of two numbers that differ by 4 (This trick only works if you have memorized or can quickly calculate the squares of numbers.If two numbers differ by 4, then their product is the square of the number in the middle (the average of the two numbers) minus 4. Let me explain this rule by taking examples 22*26 = 24^2 - 4 = 572 98*102 = 100^2 - 4 = 9996