Without calculators or pencil and paper, how will you know if a no. is divisible by 9?

Question

Tell me which ones are...which ones are not....
1) 711
2) 513
3) 821
4) 18
5) 982
6) 161
7) 621
8) 531
9) 117
10) 63

Answer 1

3, 5, and 6 are not.

A number is divisible by 9 if and only if the sum of the digits is divisible by 9. The sum of the digits are:

1) 9
2) 9
3) 11
4) 9
5) 19
6) 8
7) 9
8) 9
9) 9
10) 9

So the only numbers in the list NOT divisible by 9 are 3) 821, 5) 982, and 6) 161.

Answer 2

A number is divisible by 9 if and only if the sum of the digits is divisible by 9.
The sum of the digits are:

1) 711 = 7+1+1 = 9 (yes)
2) 513 = 5+1+3 = 9 (yes)
3) 821 = 8+2+1 =11 (no)
4) 18 = 8+1 = 9 (yes)
5) 982 = 9+8+2 =19 (no)
6) 161 = 1+6+1 = 8 (no)
7) 621 = 6+2+1 = 9 (yes)
8) 531 = 5+3+1 = 9 (yes)
9) 117 = 1+1+7 = 9 (yes)
10) 63 = 6+3 = 9 (yes)

Thus, 3, 5 and 6 are not divisible by 9

Answer 3

we can easily find out whether a no. is divisible by 9 or not.
it can be done by 2 steps
first: add the digits
second; see whether they are multiplied by 9 or not
check it out here
1) 7+1+1=9 divisible by 9
2) 5+1+3=9 " " '
3) 8+2+1=11 not divisible by 9
4) 1+8=9 divisible
5) 9+8+2= 19 not divisible
6) 1+6+1=8 " " "
7) 6+2+1=9 divisible
8) 5+3+1= 9 " " "
9) 7+1+1=9 " " "
10) 6+3=9 " " "
so, 821, 982, 161 are not divisible by 9

Answer 4

There is a strange thing about 9 that I personally found out. If the last digit is 1, the multiplicated number must end with 9. If the last digit is 2, the multiplicated number must end with 8. This is also correct as the number ascends and decends. So, that take out quite some number if you ask me. The increment is by 10. Also, you can just add 90 to the next number. So like 3x9 = 27, then 13x9 = 117. So, you just use pen and paper accordingly.

Multiplication of 9:
1)
2)
4)
7)
9)
10)

The rest aren't.

Answer 5

Another interesting thing:

111111111/9 = 12345679. Funny how that doesn't like 8.

But 1111111101/9 = 123456789.

Also, like in numerology, you can break down the numbers until you have one digit. If the last number you end up with is 9, then the number is divisible by 9. Example:

939,482,398,494

We'll start by adding each trio of numbers.

9+3+9 = 21 . . . . . 2+1 = 3
4+8+2 = 14 . . . . . 1+4 = 5
3+9+8 = 20 . . . . . 2+0 = 2
4+9+4 = 17 . . . . . 1+7 = 8
. . . . . . . V . . . . . . . . . .V
----------------------------------
. . . . . . = 72. . . . .6+12=18. . .1+8 = 9
. . . . . (7+2=9)

The result is the whole number 104,386,933,166

Answer 6

1)711 7+1+1=9 771 divisile by 9
2)513 5+1+3=9 531 divizible by 9
3)821 8+2+1=11 not divizible by 9
4)18 1+8=9 divizible by 9
5)982 9+8+2=19 not divizible by 9
6)161 1+6+1=8 not divizible by 9
7)621 6+2+1=9 divizible by 9
8)531 5+3+1=9 divizible by 9
9)117 1+1+7=9 divizible by 9
10)63 6+3=9 divizible by 9

Answer 7

Remember this.

Add all the digits of the number and if the sum is divisible be 9 then the number is divisible be 9. If the sum is divisible by 3 then the no is divisible by 3.

3, 5 & 6 not divisible by 9.

Answer 8

3) 821,
5) 982,
6) 161.

These are the number which are not divisible by 9,
the most simplest way to do it is , JUST ADD ALL THE VALUES AND IF TOTAL COMES 9 it means it is divisible by 9 for Example Take any one from your Above no.

7) 621 -----> 6 + 2 + 1 -----> 9 it means this no is divisible of 9.

And for adding i don't think so any one need calculator or pen or pencil or paper.

Answer 9

Any number that each individual number add up to 9 or 18 or 27 etc. So 711 IS divisble because 7+1+1=9; 982 is NOT divisible because 9+8+2=19.
Answers:
1) Yes
2)Yes
3)No
4)Yes
5)No
6)No
7)Yes
8)Yes
9)Yes
10)Yes

Answer 10

Add the nos and if their sum is divisible by 9 then they r too:
1) 7+1+1=9 therefore is divisible by 9
others divisible:
2,4,7,8,9,10