batch of raw materials (3/4) tons, used (2/5) on the first day, and the rest (2/7) on the second day, how many tons are left?
一批原料(3/4)吨，第一天用去(2/5)，第二天用去余下的(2/7)，还剩下多少吨？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

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

<gadget id="calculator">(3/4) * (2/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(3/4) - (3/10)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(9/20) * (2/7)</gadget>
<output>9/70 = around 0.128571</output>

<gadget id="calculator">(3/4) - (3/10) - (9/70)</gadget>
<output>9/28 = around 0.321429</output>

<result>9/28 = around 0.321429</result>