Option 1 -> This is the total product after the change, not the average product.
Option 2 -> This is the average product before the change (40÷3=13.33), not after.
Option 3 -> Average Product = Total Product ÷ Labor = 50 ÷ 4 = 12.5.
Option 4 -> This is the total product before the change, not the average product.
Hence, Option 3: 12.5 -> The average product (AP) is calculated by dividing the total product by the quantity of labor used. After the change, we have 4 units of labor producing 50 units of total product. Therefore, AP = 50 ÷ 4 = 12.5 units per worker. This measures the productivity per unit of labor after the change. -> correct