If these are the only four sellers in the market, then when the price decreases from $4 to $2, the market quantity supplied

Decreases by 50 percent

Explanation:

The law of supply asserts that other things remaining constant, the quantity of goods and services supplied increases as price rises. Therefore, the price and quantity supplied are directly related. Should the price fall, the quantity supplied will also decrease. Producers will prefer to supply more when the price is high to make more revenue.

The supply curve is upward sloping indicating how quantity supplied changes at different price levels. In the case, the price has decreased from $4 to $2, which represents a 50 percent drop. The quantities supplied will decrease as per the law of supply. A 50 percent decrease may result in a similar decrease in quantity supplied as the supply curve is upward sloping.