A bundle of wires is 100 meters long. The first time (1/4) of the full length is used, and the second time (2/5) of the full length is used. How many meters are left unused?
一捆电线长100米，第一次用去全长的(1/4)，第二次用去全长的(2/5)，还剩多少米没有用？
<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>

<gadget id="calculator">100 * (7/20)</gadget>
<output>35</output>

<result>35</result>