Storing Variables As Arrays - Code

I have the following code for a user-defined function:

Function SeriesSum2(A, B, x, C, D, y, z, Num)

Summation = 0

For i = 1 To Num

Summation = Summation + (((A - B) * (((0.01 * B / (A - B)) _
^ (1 / (y - 1))) ^ i) + B - x) / ((1 + x) ^ i))

Next i

Product = 1

For i = 1 To Num

Product = Product * (1 + ((C - D) * (((0.01 * D / (C - D)) _
^ (1 / (z - 1))) ^ i) + D))

Next i

SeriesSum2 = WorksheetFunction.SumProduct(Summation, Product)

End Function

To simplify, suppose Num = 3, and the three terms of Summation are {3, 5, 9}. Call these S1, S2, S3. Further, suppose the first three terms of Product are {1, 4, 12}. Call these P1, P2, P3.

My desired result of the function is 3*1 + 5*4 + 9*12 = 131. Instead, I'm getting 3*12+5*12+9*12 = 204. That is, the function is returning S1*P3+S2*P3+S3*P3, while I want S1*P1+S2*P2+S3*P3.

Can anyone instruct me as to what I need to do to get my desired result? I'm guessing it has something to do with storing Product as an array, but I'm a very novice VB'er, so I'm not sure.

Of course, if there are any other glaring errors in my code,