A number divide by 11

Math is really fun. We can easily find out where a number is divisible with 11 or not. What we have to do.. we have to put (or imagine) alternate + and - signs in front of the digits and then sum up. If the result is 0 or dividable by 11, then the number will divide by 11. e.g.
235698
so, +2 -3 +5 -6 +9 -8 = -1
235698 will not divide by 11. But if the number is,
235697
so, +2 -3 +5 -6 +9 -7 = 0
235698 will divide by 11.