A glass of milk is 200ml, drank (1/4), how many ml is left in the glass
一杯牛奶200毫升，喝了(1/4)，杯中还有多少毫升
<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">200 * (3/4)</gadget>
<output>150</output>

<result>150</result>