You need to add (): Excel divides and multiplies before it adds and substracts.
(A1+A2)/10 -- Excel will 1st add then divide the result of the addition.

"TDF" wrote:

when i add 2 numbers then divide by a number it's answer is wrong, why

example: when i add 500 = A1
100 = A2
=A1 + A2/10 answer comes back as 150