After 75% of 4 tons of chemical fertilizers are used up, 0.75 tons are used up, how many tons are left
4吨化肥用去75%后，又用去0.75吨，还剩下多少吨
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">4 * (1/4)</gadget>
<output>1</output>

<gadget id="calculator">1 - 0.75</gadget>
<output>0.25</output>

<result>0.25</result>