Process Costing

This is a BPP MCQ. A manufacturer produces Product X from three input raw materials, P, Q and R. There is some loss in the process, usually about 5% of input. Results for the most recent month are as follows. Input 5000kg of P, cost of $15000 2000kg of Q, cost of $8000 1000kg of R, cost of $8000 Output 7500kg of Product X Which one of the following performance measurements is accurate? A) Rate of wastage = 6.7% B) Average cost of input = 4.13 per kg C) Output: input conversion ratio = 6.25% D) Materials yield variance = $1938(A) The correct answer is B. I think this should be average cost of output. Help me, Sir.