Xiao Ming read a book, and he read (1/5) in the first 3 days. At this speed, how many days will it take to finish reading.
小明读一本书，前3天读了(1/5)．照这样的速度，还要读多少天才能读完．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 3</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>