How do you tell when a number is divisible by 11
Add the digits using alternating signs.....if the result is 0, the number is divisible by 11
Example ....121 = 11^2
So
+1 -2 + 1 = -1 + 1 = 0
We could also start wih a negative sign
132 = 11 * 12
-1 + 3 - 2 = 2 - 2 = 0
