Hi, new to the forums and I am trying to resolve a dispute that has arrisen at work. Can anyone point me to the mathmatical proof for the following:

If you:

Take any two digit number (eg 38)

sum the two digits from this number (3+8 = 11)

Subtract the result from the origional number (38-11 = 27)

The answer will always be a multiple of 9.

Can someone show me why this is always the case?

Much appreciated.