A pile of rice (9/10) tons, (1/10) of the pile of rice is removed for the first time, and (2/5) of the pile of rice is removed for the second time. What fraction of this pile of rice is left?
一堆大米(9/10)吨，第一次运走这堆大米的(1/10)，第二次运走这堆大米的(2/5)．还剩下这堆大米的几分之几？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) + (2/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>