Mingming reads an extra-curricular book. He read 17 pages on the first day, 23 pages on the second day, and 20 pages on the third day. How many pages does he read on average every day?
明明读一本课外书，第一天读了17页，第二天读了23页，第三天读了20页，他平均每天读多少页．
<gadget id="calculator">17 + 23 + 20</gadget>
<output>60</output>

<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<result>20</result>