for edexcel, you don't calculate it like that.
You combine the two marks together and THEN it is divided by 120 for a UMS.
E.G. you got 40/50 for prac, and you got 40/50 for your unit 6 exam. Thats 80/100. Maybe the boundary requires a 82/100 for an A, so you get a B, which is around 90/120.