Doubling the Numbers

H.D. Motiramani

 

“Doubling” any number is achieved by multiplying the number by 2.

In other way, adding a number to itself. So, doubling can be done by repeated addition or multiplication by two, whichever is comfortable!

 

Example --- Double of 45 is      45 X 2      (or)       45+45 =90

Double of the number by repeated addition:

 27 +  27 = 25+25  + 2 +2  = 54

77  + 77  = 75+ 75 + 2 + 2 = 154

626 + 626 = 1200 + 40 + 12 = 1252

3278 + 3278 = (3200 + 3200) + (70+70) + (8+8) = 6400 +140 + 16 = 6556

 

Another little trick is to “Break & double”

For example take a number 694826

69 48 26 = 158  96  52 = 1589652

Another Example: double of 36554

365 54 = 730 I 108       =  731 I 08    =   73108

Note here that Right Hand Side that is 108  is to be in two digits because doubling of 54 was of two digits. Therefore 1 from 108 has been carried to left to make 730 as 731.

 

Doubling has an advantage that for multiplication by 4, doubling can be done two times and in case of multiplication by 8 it needs to be done three times.

Example 43×4

Double of 43 = 86

Double of 86 = 172

Therefore 43×4 =172

If we wanted to get the answer of 43×8, we need to double 172 again.

Double of 172 that is 17 2  is 34 4 = 344. So 43×8 = 344

 

 

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