If a typist types a manuscript, after 15 hours of typing, there is still (1/4) left, how many hours will it take to finish typing.
打字员打一部书稿，打了15小时后，还剩(1/4)，则剩下的还需多少小时打完．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<result>5</result>