Dear, Whom this may concern
I'm stuck in class in Yr 7 And I'm finding it hard on our new topic Divisibility! When I try to find out what this means on Internet sites i can not understand the used symbols like algebra and so on. I'm stuck on the divisibility rules for the number 11! I have found the divisibility rule for 7 and wondered if this was write
7 is Divisible by taking the last digit of the number, doubling it and then subtracting the doubled number from the remaining number. If the number is evenly divisible by seven, the number is divisible by seven!
That is how I like to see my answers on the Internet ( written out not using symbols and signs)! If you could get in touch with me I would be grateful!
From Concerned Child
Tammy
Hi Tammy,
Your rule fro divisibility by 7 is correct. Thus, for example if the number is 4102 then
410 - 2
2 = 406
so 4102 is divisible by 7 if 406 is divisible by 7. To decide if 406 is divisible by 7 you can apply your rule again.
40 - 2
so 406 is divisible by 7 if 28 is divisible by 7. But 4 7 = 28 so 28 is divisible by 7, and hence 406 is divisible by 7, which insures 4102 is divisible by 7.
For a test of divisibility by 11 start from the right and add every second digit. Now subtract from that total the sum of the remaining digits. The resulting number is divisibly by 11 if and only if the number you started with is divisible by 11.
For example consider 678234.
(4 + 2 + 7) - (3 + 8 + 6) = 13 - 17 = -4
which is not divisible by 11 so 678234 is not divisible by 11. Now try 908193
(3 + 1 + 0) - (9 + 8 + 9) = -22
which is divisible by 11 so 908193 is divisible by 11.
Penny