HOW CAN WE KNOW THAT A GIVEN NUMBER IS DIVISIBLE BY 7 OR NOT?
2006-09-21 03:19:41 · 7 answers · asked by nats 1 in Science & Mathematics ➔ Mathematics
multiply the last digit by 2,
subtract it from the remaining digits,
if the resulting difference is divisible by 7,
then it is divisible,
else, it is not divisible
ex.
1. 91 (9 - 1x2 = 7, divisible)
2. 133 (13 - 3x2 = 7, divisible)
note: 0 and negative numbers that are divisible are considered as divisible
2006-09-21 03:31:23 · answer #1 · answered by David W 2 · 5⤊ 1⤋
The person who said that there was no rule, because 7 is prime, was wrong.
The rule is to alternately add and subtract triplets, working from the right. To see if 3 654 310 332 is divisible by 7, do 332 - 310 + 654 - 3. It comes to 673, which does not divide by 7, so neither does the number we started with. I think the other answerers are correct that doing the division is just about as easy.
2006-09-21 14:03:31 · answer #2 · answered by bh8153 7 · 0⤊ 0⤋
Yes, there is a divisibility rule for the number 7. But from my experience in math competitions, I think it is faster to just try dividing by 7 than it is to use the rule.
If you're still interested, it is definitely easy to find. Just look it up in a math reference or online.
2006-09-21 16:58:44 · answer #3 · answered by Math_Guru 2 · 0⤊ 0⤋
Try it and see? Subtract a known multiple of 7 that happens to be close to your number away from it and see if the remainder is divisible by 7?
Example Number is 654310332
subtract 777777777 from it to get -12367445
still inconveniently big? add 15555554 to get
3188109 , hm subtract 1555554 twice, result is
77001 you know that this does not divide by 7.
2006-09-21 10:35:41 · answer #4 · answered by Anonymous · 0⤊ 2⤋
7 is a prime number. So there isn't a divisibility rule as such. You have to divide and check..
2006-09-21 10:31:21 · answer #5 · answered by noesis 2 · 0⤊ 1⤋
no easy specific divisibility rule.better to divide and see.the div rule is more complicated than the actual division
2006-09-21 10:21:58 · answer #6 · answered by raj 7 · 0⤊ 0⤋
not any actually.dere is one,but it is much more complex than the actual division.
divide the answer u can be more sure that way.
2006-09-21 11:45:08 · answer #7 · answered by Anonymous · 0⤊ 1⤋