A number divide by 7

Math is really fun. We can easily find out where a number is divisible with 7 or not. What we have to do.. we have to take off the last digit and multiply it by 2. Then subtract the result from the digits you have left.If the result is 0 or dividable by 7, then the number will divide by 7. e.g.
786234
Take off the last digit...that is 4.
Multiply by 2 .... 4*2=8
Subtract this from the other digits....(78623-8)=78615
do the same thing again and again until u get a good number that is divisible by watching the number.

One more method: its applicable only if the number is having more than 2 digit.What we have to do..we have to take off the last two digit and multiply the remaining digits by 2. Then add the result with the number that was taken off. Now check whether the result is divisible by 7 or not. e.g.
2723
Take off last two digit: 23
Multiply by 2 with remaining number: 27*2=54
Then add: 54+23=77
so,2723 is divisible by 7.