A glass of water, the first time I drank the full glass (1/4), the second time I drank the full glass (2/5), what percentage of the glass is the rest?
一杯水，第一次喝了全杯的(1/4)，第二次喝了全杯的(2/5)，剩下的占这杯水的几分之几？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>