When 6 units of labour (or variable factor) are employed:
TP = AP × L = 25 × 6 = 150
Also, TP = ∑MP = 50 + 40 + 30 + 20 + 10 + 0 = 150
AP = TP/L = 150/6 = 25
MP of 6th unit = TPn – TPn-1 = 150 – 150 = 0
Likewise, when 7 units of labour are employed:
TP = AP × L = 21 × 7 = 147
Also, TP = ∑MP = 50 + 40 + 30 + 20 + 10 + 0 – 3 = 147
AP = TP/L = 147/7 = 21
MP of 7th unit = TPn – TPn-1 = 147 – 150 = – 3