There are 20 story books and 30 picture books. (3/5) of the story books is equal to the number of picture books.
故事书有20本，图画书有30本，故事书的(3/5)等于图画书的多少．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) / 30</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">20 * (1/50)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>