There are (17/20) tons of yellow sand on the construction site, (1/4) is used in the morning, and (2/5) is used in the afternoon. What fraction of this pile of yellow sand is left?
工地有黄沙(17/20)吨，上午用去(1/4)，下午用去(2/5)，还剩下这堆黄沙的几分之几？
<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>