How do you....?

"To determine if a number is divisible by 7, take the last digit off the number, double it, and subtract the doubled number from the remaining number. If the result is evenly divisible by 7 (e.g. 14, 7), then the number is divisible by seven. This may need to be repeated several times."

Funny you should ask this heh

When I was a kid, I learned the "easy" way to tell if a number was divisible by just about every single digit number. The only problem is, if there is an easy way to do 7, I could never remember it. I poked at it for a long time, and finally came up with something, but I'm not sure it is much/any easier than just dividing by 7. Here goes...

Take your number. Remove the last digit. Double that digit, and subtract it from "the rest" of the number (i.e. what you had left after you removed the last digit). Keep doing that until you get to a small enough number that you can trivially divide it by 7. If that last number is divisible by 7, then the original number was divisible by 7.

Example: 7777 (which clearly is divisible by 7)

777 - (2 * 7) = 763

76 - (2 * 3) = 70

7 - (2 * 0) = 7

7 is divisible by 7, therefore 7777 is.

12345 (which I'm about to figure out if it is divisible by 7)

1234 - (2 * 5) = 1224

122 - (2 * 4) = 114

11 - (2 * 4) = 3

3 is not divisible by 7, therefore 12345 is not.

Divide it by 7. Man, these people have the hardest methods.

Here, take the number 34,985. You want to know if it's divisible by 7 without all that?

34,985/7=4,997.86

It's not a whole number, so it's not divisible by 7. There's a fraction of a whole number as a remainder (decimal).

Or take it the long way. Of course I don't have the symbols on my keyboard to do it that way, but I can run you through the steps:

1.) 34/7=4 r6~bring down the 9

2.) 69/7=9 r6~bring down the 8

3.) 68/7=9 r5~bring down the 5

4.) 55/7=7 r6~you have a remainder and there's nothing left to bring down, then it's not divisible by that number. If you finish this last step and you have a 0 where that last 6 is then it is divisible.

take the last digit of the number, double it, then subtract it from the remaining numbers.

For eg. is 345 divisible by 7?

double 5, 10.

subtract ten from 34, you get 24. Is 24 divisible by 7? No. So 345 isn't divisible by 7.

P.S. you can repeat the process for bigger numbers.

P.P.S. In the case when you subtract and get a negative number take the absolute value.

P.P.P.S. If the answer after subtracting is 0, then the number is divisible by 7.

There are 2 ways that I know of

1--(the method that is being posted) Remove the last digit and double it. Then subtract the doubled number from remaining number.

8715 becomes 871 -(5*2) =861

861 becomes 86-(1*2) = 84

84 becomes 8-(4*2) = 0

The other method is similar to determining if a number is divisible by 11. But instead of adding and subtracting every other number, you add and subtract every other group of three.

475, 412,392 becomes 475 -412 +392 = 455

because 455 is divisible by 7, the original number is too.

Well divide it by 7, in yr head if u can, with a caluculator if not. Or if it's something obvious like 7 or 14 then 0 like 70,140 obvious it's divisible by 7. On a calc. type 7 then x then = and u shud get numbers divisible by 7.

If 7 goes into it evenly without a remainder then it is divisable by 7.

Divide it by 7; if there is no remainder, then it is divisible by 7

Take the number and divide it by 7? Or, if it's a multiple of 7 like 14, 21,49 ect.

divide that number by seven and see if the result is a whole number if not it isn't divisible