Mr. Liu moved a batch of books, 15 books at a time, and moved 4 times, exactly half of the books were moved. The rest of the books are moved 20 each time, how many times will it take to finish moving.
刘老师搬一批书，每次搬15本，搬了4次，正好搬完这批书的一半．剩下的书每次搬20本，还要多少次才能搬完．
<gadget id="calculator">4 / 20</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

<result>3</result>