A pile of sand weighs (9/4) tons, and the rest is used (4/5), how many tons are left.
一堆沙子重(9/4)吨，剩下的是用去的(4/5)，剩下多少吨．
<gadget id="calculator">9 / 4</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 + (4/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">(9/4) / (9/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(9/4) - (5/4)</gadget>
<output>1</output>

<result>1</result>