Shortcut-2

To multiply any number by “13”

Let’s take an example:

221 * 13

Step – 1:

Take “0” on left and right hand side of other number:

Thus,

We get:

02210

Step – 2:

Now, make pairs of two:

“02210”

We get:

“02” ... “22” ... “21” ... “10”

Now, multiply first digit of all pairs by “3” and add the result on right side.

Thus, we get:

“02” = (0*3) + 2 = 2

“22” = (2*3) + 2 = 8

“21” = (2*3) + 1 = 7

“10” = (1*3) + 0 = 3

Hence,

Answer is:  

(221 * 13) = 2873

Let’s take more examples.  

5301 * 13

Step – 1:

Take “0” on left and right hand side.

Thus, we get:

“053010”

Step- 2:

Make pairs:

“053010”

Thus, we get:

“05” ... “53” ... “30” ... “01” ... “10”

Multiply right hand side number by “3” and add the result to right hand side.

“05” = 0 * 3 + 5 = 5

“53” = 5 * 3 + 3 = 18

“30” = 3 * 3 + 0 = 9

“01” = 0 * 3 + 1 = 1

“10” = 1 * 3 + 0 = 3

Hence, we would get:

5 (18) 9 1 3

Take carry “1” of (18):

Hence, Answer is:

68913

756 * 13

Step – 1:

Take “0” on Left and Right hand sides.

WE would get:

“07560”

Step – 2:

Make pairs of “07560”

Thus,

“07” ... “75” ... “56” ... “60”

Now, multiply first digit of all pairs by “3” and add the result on right side.

“07” = 0 * 3 + 7 = 7

“75” = 7 * 3 + 5 = 26

“56” = 5 * 3 + 6 = 21

“60” = 6 * 3 + 0 = 18

We would get:

7 (26) (21) (18)

Take carries starting from right hand side:

7 (26) (22) (8)

7 (28) (2) (8)

9 (8) (2) (8)

Hence,

Answer is:

756 * 13 = 9828