Question

divisibility rules by 10 to 20​

Answer 1

Answer:

10 - if a number divisible by both 2,5 then

it divisible by 10

20 - if a number divisible by both 4,5 then

it divisible by 20

Answer 2

Answer:

Divisible by 10

Last digit must be 0.

Ex : 456780 is divisible by 10 –> last digit is 0.

78521 is not divisible by 10 –> last digit is 1.

Divisible test of 11

Form the alternating sum of digits. The result must be divisible by 11.

Ex : 416042 is divisible by 11 –> 4-1+6-0+4-2 = 11, 11 is divisible by 11.

8219543574 is divisible by 11 –> 8-2+1-9+5-4+3-5+7-4 = 0 is divisible by 11.

Divisibility by 12

The number must be divisible by 3 and 4. Because (3* (2^2)) are prime factors of 12.

Ex : 462157692 is divisible by 12 –> last 2 digits 92, so divisible by 4, and sum 4+6+2+1+5+7+6+9+2 = 42 is divisible by 3.

625859 is not divisible by 6 –> last 2 digits 59, is not divisible by 4. No need to check for 3.

Divisibility test for 13

Multiply last digit with 4 and add it to remaining number in given number, result must be divisible by 13. (You can again apply this to check for divisibility by 13.)

Ex :

1. 4568 is not divisible by 13 –> 456 + (4*8) = 488 –> 48 + (4*8) = 80, 80 is not divisible by 13.

2. 593773622 is given number. 2 is last digit. add 4*2 to 59377362 -> 59377370

    5937737+ (4*0) = 5937737, we cannot tell that this result is divisible by 13. So, we do it again.

    593773 + (4*7) = 593801, we will do it again.

    59380 + (4*1) = 59384, we will do it again.

    5938 + (4*4) = 5954, we will do it again.

    595 + (4*4) = 611, we will do it again.

61 + (4 *1) = 65 , 65 is divisible by 13.

    So, 593773622 is divisible by 13.

Don’t forget to check the generalized rule at the end.

Divisibility by 14

The number must be divisible by 2 and 7. Because 2 and 7 are prime factors of 14.

Divisibility rule of 15

The number should be divisible by 3 and 5. Because 3 and 5 are prime factors of 15.

Divisible rule for 16

The number formed by last four digits in given number must be divisible by 16.

Ex : 7852176 is divisible by 16 –> 2176 is divisible by 16.

Divisibility by 17

Multiply last digit with 5 and subtract it from remaining number in given number, result must be divisible by 17. (You can again apply this to check for divisibility by 17.)

Follow the similar examples given in divisibility by 7 and divisibility by 13.

Divisibility by 18

The number should be divisible by 2 and 9. Because (2*(3^2)) are prime factors of 18.

Divisibility by 19

Multiply last digit with 2 and add it to remaining number in given number, result must be divisible by 19. (You can again apply this to check for divisibility by 19.)

Follow the similar examples given in divisibility by 7 and divisibility by 13.

Divisibility by 20

The number formed by last two digits in given number must be divisible by 20.

Ex : 2374680 is divisible by 20          –>      80 is divisible by 20.

456215789654824 is not divisibility by 20    –>     24 is not divisibility by 20.