MATHEMATICS

Rabu, 09 Januari 2013

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

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