3. If the price falls to $10, the quantity sold decreases to 10 a day. The producer surplus decreases to

(the area of the blue triangle in Figure 3 ). The change in producer surplus is a decrease of $75 (from $100 down to $25).

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$15 − $10 = $5 

($15 − $5) × 20 ÷ 2

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$15 × 20 = $300

$300 − $100 = $200 

($10 − $5) × 10 ÷ 2 = $25

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Figure 3 Solution to In the News