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Sunday, 30 March 2014

DIVISIBILITY OF NUMBERS BY 20 to 23

Divisibility rule for 20:

The no whose last two digits are divisible by 20 is divisible by 20.

5580 : 80 is divisible by 20

Divisibility rule for 21:

If the number is divisible by 3 and 7, then the number is divisible by 21

Divisibility rule for 22:

If the number is divisible by 2 and 11, then the number is divisible by 22

Divisibility rule for 23:

Multiply unit place by 7(Key no of 23) add it to rest of the digits.

For 1 5 1 5 7x 7

4 9

                                                -----------------------------

                                                        1 5 6 4 x 7

                                                           2 8

                                                ------------------------------

                                                       1 8 4 x 7

                                                       2 8

--------------------------------

4 6:So 12468 is not divisible by 23

Monday, 24 March 2014

DIVISIBILITY OF NUMBERS BY 14 to 19

By 14:

If the number is divisible by 2 and 7, then the number is divisible by 14

By15:

If the number is divisible by 3 and 5, then the number is divisible by 15

By 16:

If the last four digits of the number is divisible by 16, then the number will be divisible by 16.
e.g.- 67891888 : Since 1888 is divisible by 16,So the number is divisible by 16.

By 17:

Multiply unit place by 12(Key no of 17) add it to rest of the digits.

for key number: 17 x 7=119 , key no. = 11+1=12

DIVISIBILITY OF NUMBERS BY 10 to 13

BY 10

The no having 0 in its unit place is divisible by 10.
6679 : 9 is unit digit place ,So 6679 is not divisible by 10.
4570 : 0 is unit digit place ,So 4570 is not divisible by 10.

BY 11

The no whose difference of sum of every other digit
is divisible by 11.
14568:(1+5+8)-(4+6)=4
So it is not divisible by 11.
1331:(1+3)-(1+3)=0
So it is not divisible by 11.