For example the rule for divisibility by 9 is that if the sum of the digits of a number is divisible by 9, then the number itself is divisible by 9.
2006-09-26 00:42:29 · 7 answers · asked by small 7 in Science & Mathematics ➔ Mathematics
The bottom line is that dividing the number by 7 is actually easier and quicker than any of the aforementioned "rules"
2006-09-26 01:21:18 · answer #1 · answered by MollyMAM 6 · 1⤊ 0⤋
Dividing by 7
To find out if a number is divisible by seven, take the last digit, double it, and subtract it from the rest of the number.
Example: If you had 203, you would double the last digit to get six, and subtract that from 20 to get 14. If you get an answer divisible by 7 (including zero), then the original number is divisible by seven. If you don't know the new number's divisibility, you can apply the rule again.
Matthew Correnti describes this method:
If you do not know if a two-digit number, call it ab, is divisible
by 7, calculate 2a + 3b. This will yield a smaller number, and if
you do the process enough times you will eventually -- if the
number ab is divisible by 7 -- end up with 7.
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2006-09-26 00:47:37 · answer #2 · answered by hmmm 3 · 2⤊ 1⤋
Division by 7
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Method 1
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Divide the number in groups of 3 numbers starting from the right side. Now substract and add the numbers as in the example below:
7768124 divisible by 7?
Step 1: 7 | 768 | 124
Step 2: 124 - 768 + 7 = -637
637 is divisible by 7 so 7768124 is also divisible by 7.
Method 2
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It's an algorithm repeat this step until no numbers are left:
1. Get the last digit
2. Multiple it by 2
3. Substract it from the new number
Example:
7768124, 4 goes off. We have to substract by 2*4=8
776812 - 8 = 776804, 4 goes off, 2*4=8
77680 - 8 = 77672, 2 goes off, 2*2=4
7767 - 4 = 7763, 3 goes off, 2*3=6
776 - 6 = 770, 0 goes off, 2*0=0
77 - 0 = 77
77 is divisible by 7! So 7768124 is also divisible by 7.
2006-09-26 00:50:32 · answer #3 · answered by cirijazz 1 · 4⤊ 0⤋
You might try subtracting 1001
from a large number
until you get a small number
example - 123456788
23356788
13346788
3336788
2335788
1334788
333788
233688
133588
33488
23478
13468
3458
2457
1456
455
455 is divisible by 7, so the original number was divisible by 7
2006-09-26 01:09:08 · answer #4 · answered by bob h 3 · 1⤊ 0⤋
. to make sure if a kind is divisible through 7, double the superb digit, then subtract it from the superb digits of the kind. in case you get an answer divisible through 7, then the unique variety is divisible through 7. in case you do not understand no matter if the recent variety is divisible through 7, you note the rule of thumb again. as an celebration, to envision no matter if 616 is divisible through 7, double the superb digit (6 x 2 = 12), then subtract the reply from the superb digits (sixty one – 12 = 40 9). because 40 9 is divisible through 7, so is 616
2016-11-24 19:55:51 · answer #5 · answered by ? 4 · 0⤊ 0⤋
If you multiply seven by a number and then divide the product by the same number you will get seven.
2006-09-26 01:03:20 · answer #6 · answered by uselessadvice 4 · 0⤊ 0⤋
I don`t think there`s any for 7.Sorry
2006-09-26 00:43:50 · answer #7 · answered by ioana v 3 · 0⤊ 2⤋