HoW do you find the divisivility rule for 7?

Answer 1

How you FIND it is a bit complicated. You have to do modulo arithmetic. If you just want to KNOW the division rule for 7, it goes like this : subtract double the final digit of a number from the other digits. Repeat until you can tell whether the answer divides by 7 or not. Example : Does 4587 divide by 7 ? Compute 458 - 7x2 = 444. You still can't tell, so do it again. Compute 44 - 4x2 = 36. Now you know 36 doesn't divide by 7, so neither does 4587. Example : Does 2233 divide by 7 ? Compute 223 - 3x2 = 217. You still can't tell, so do it again. Compute 21 - 7x2 = 7. Now you know that 7 does divide by 7, so does 2233.