You have to use next year's cost as you're planning for next year pricing
You have to compare the material usage for various demands, both either using the existing materials or using the cheaper alternatives.
You have to present your answer something like this:
Calculation of next year's cost per unit and total fixed overheads
Price £80 £84 £88 £90 £92 £96 £100
Demand 25 23 21 20 19 17 15
(000's)
Variable Cost of manufacturing per unit
-original material
-substitution (remember to include the inspection)
find the contribution per unit at each price for
-original material
-substitution (remember to include the inspection)
find the total contribution at each price according to the quantity demanded for
-original material
-substitution (remember to include the inspection)
pick the highest for each material for highest contribution
afterwhich, deduct the fixed costs (fixed overheads and the additional fixed inspeaction costs)
calculate the profit for each material
decide between the materials which is getting more profit
for b) it is easier to use the graphic method or find out the equation
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hope this helps as I cleared my f5 last Decemeber and hasnt touch anything close to it since then.