There are 3 tons of chemical fertilizers, and (1/4) of them are transported away on the first day, and (2/5) of them are transported away on the second day.
有3吨化肥，第一天运走它的(1/4)，第二天运走它的(2/5)，还剩这批化肥的多少没有运．
<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>