DIVISIBILITY OF NUMBERS BY 7,8&9

BY 7

First let’s Know about the
KEY NUMBER

for 7 : 7 X 7 = 49     : So Key no is 4 + 1 = 5
for 13 : 13 X 3 = 39  : So Key no is 3 + 1 = 4
it is especially important for PRIME NUMBERS. NOW

Divisibility rule for 7:

Multiply unit place by 5 add it to rest of the digits.
for 12468 : 

8 x 5      :40+1246=1286 

6 x 5      :30+128=158

8 x 5      :40+15=55

55  :So 12468 is not divisible by 7

BY 8

The no whose last three digits are divisible by 8 is divisible by 8.

12565588 : 588 is not divisible by 8
So 12565588 is not divisible by 8.

BY 9

The no whose sum of digits are divisible by 9

e.g.- 9456 : 9+4+5+6=24 : 2+4=6
which is not divisible by 9 ,So 9456 is not divisible by 9

        3858 : 3+8+5+8=24 : 2+4=6
which is not divisible by 9 ,So 3858 is not divisible by 9