Hi,
I have this challenge where I would like to calculate the average of product time across products (a, b, c).
The simple avg function gives me the average (10 + 100 + 300) / 3 = 137.
But i want the weighted average where sales quantity is taken into account: (10/90)*10 + (30/90)*100 + (50/90)*300 = 201.
How do i write an expression for this?`
/ Michael
| year | month | product | sales quantity | product time |
| 2016 | august | a | 10 | 10 |
| 2016 | august | b | 30 | 100 |
| 2016 | august | c | 50 | 300 |
| | | 90 | |
