A colored ribbon is 4m long, if (1/4) is used up, how much m is left?
一条彩带长4m，用去(1/4)，还剩多少m．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">4 * (1/4)</gadget>
<output>1</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<result>3</result>