Is there a number to test that a number is divisible by 7? The Magic rule of 7 if you would like to call it that???
2006-10-02 14:45:23 · 1 answers · asked by lint 1 in Education & Reference ➔ Trivia
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, 0, -7, etc.), then the number is divisible by seven. This may need to be repeated several times.
Example: Is 3101 evenly divisible by 7?
Split 3101 into 310 and 1.
Double that last digit: 1 -> 2
Now you have 310 and 2.
Subtract: 310 - 2 = 308
So, it's divisible by 7, because 308 is divisible by 7!
How do I know 308 is divisible by 7? Same thing!
308 -> 30 and 8
-> 30 and 16
-> 30 - 16 = 14
14 is divisible by 7.
2006-10-02 14:48:53 · answer #1 · answered by PJ 3 · 1⤊ 0⤋