A steel bar is 28 meters long, if (1/4) of it is used up, how many meters are left useless?
一根钢筋长28米，用去它的(1/4)，还剩多少米没用？
<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">28 * (3/4)</gadget>
<output>21</output>

<result>21</result>