Multiplication of 2 two-digit numbers

Multiplication of 2 two-digit numbers where the first digit of both the numbers are same and the last digit of the two numbers sum to 10

Example

 To calculate 56 x 54

Multiply 5 by 5+1. So, 5 x 6 = 30. Write down 30.

 Multiply together the last digits: 6 x 4 = 24. Write down 24.

 The product of 56 and 54 is thus 3024.

 

Multiplication of two numbers that differ by 2

 (This trick only works if you have memorized 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.

Example

 18 x 20 =( 19 x 19) - 1 = 361 - 1 = 360

 25 x 27 = (26 x 26) - 1 = 676 - 1 = 675

 49 x 51 = (50 x 50 ) - 1 = 2500 - 1 = 2499

 

 

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.

 Example

 22 x 26 = (24 x 24 ) - 4 = 572

 98 x 102 = ( 100 x 100) - 4 = 9996

 148 x 152 = (150 x 150) - 4 = 22496

 

Multiplication of two numbers that differ by 6

(This trick only works if you have memorized or can quickly calculate the squares of numbers.

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

 Example

 10 x 16 = (13 x 13) - 9 = 160

 22 x 28 = (25 x 25) - 9 = 616