(1/25) meter of rope, how many meters will be used after (1/2) is used up, leaving (1/1000) meter.
(1/25)米的绳子，用去(1/2)后再用去多少米，剩(1/1000)米．
<gadget id="calculator">1 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/25) * (1/2)</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">1 / 1_000</gadget>
<output>1/1_000 = around 0.001</output>

<gadget id="calculator">(1/25) - (1/50) - (1/1_000)</gadget>
<output>19/1_000 = around 0.019</output>

<result>19/1_000 = around 0.019</result>