Multiplication Of Two Numbers That Differ By A Certain Number

 

Multiplication Of Two Numbers That Differ By 2

This trick only works if you have memorised or can quickly calculate the squares of numbers. When two numbers differ by 2, their product is always the square of the number in between these numbers minus 1. Let’s explain this rule by taking examples:

18*20 = 19^2 - 1 = 361 - 1 = 360

25*27 = 26^2 - 1 = 676 - 1 = 675

Multiplication Of Two Numbers That Differ By 4

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’s explain this rule by taking examples

22*26 = 24^2 - 4 = 572

98*102 = 100^2 - 4 = 9996

Multiplication Of Two Numbers That Differ By 6

If the two numbers differ by 6, then their product is the square of their average minus 9

Let’s explain this rule by taking examples

10*16 = 13^2 - 9 = 160. Here the average of 10 and 16 is 13, hence the answer is 13 square minus 9, i.e. 13^ - 9 = 160

22*28 = 25^2 - 9 = 616. Similarly, here the average is 25, hence, 25 square minus 9 = 616 is the answer