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