- 19

- 0

I don't know how to work with this divisibility stuff when it's generalized to numbers like x+y+z. I don't even know where to begin. All I can do is "9w = x+y+z for some number w"...and now I don't know where to go. If I think up example values for x,y, and z I find that (a) keeps working, but I don't know why. Any help appreciated!Given x, y and z such that x+y+z is divisible by 9, which of the following must also be divisible by 9?

a) 100x + 10y + z + 9

b) 10y + z + 9

c) 9x + 90y + z + 9

d) x + y + 9z + 9

e) 100x + 10y + 7z