b. average product must be decreasing if the marginal product of labor is less than the average product of labor. Since the marginal product is declining with an increase in labor input, the average product of labor will tend to decline when the marginal product of labor curve is lower than the average product of labor curve, or when the MPL APL.
The average product of labor must be rising anytime the marginal product of labor exceeds the average product of labor.
Thus, we can conclude that the marginal product of labor is lower than the average product of labor while the average product of work is declining.
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