Just t-testing

You made quick comparisons between groups of data, but you want to know whether the modeled data you created differ significantly from your original sales.

This is a good situation to use a t-test, which you can call with the function T.TEST(). Remember that T.TEST() takes four arguments: the two ranges, and then a 'tails' and 'type' argument. These latter two arguments you can specify simply with an integer.