Zhang Ming read an extracurricular book in 10 days. He read an average of 43 pages a day in the first 5 days, and an average of 57 pages a day in the next 5 days. How many pages does this extracurricular book have?
张明用10天看完一本课外书，前5天平均每天看43页，后5天平均每天看57页．这本课外书一共有多少页？
<gadget id="calculator">43 * 5</gadget>
<output>215</output>

<gadget id="calculator">57 * 5</gadget>
<output>285</output>

<gadget id="calculator">215 + 285</gadget>
<output>500</output>

<result>500</result>