Xiao Ming reads a 320-page story book, and reads 20 pages a day for the first 4 days. If he wants to read the rest within 8 days, how many pages do he need to read on average every day?
小明看一本320页的故事书，前4天每天看20页，剩下部分如果要在8天内看完，平均每天要看多少页？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">320 - 80</gadget>
<output>240</output>

<gadget id="calculator">240 / 8</gadget>
<output>30</output>

<result>30</result>