The fruit wholesale station bought (9/10) tons of fruit, sold (1/5) tons in the first week, and sold (3/10) tons in the second week. How many tons are left unsold?
水果批发站新进(9/10)吨水果，第一周卖出(1/5)吨，第二周卖出(3/10)吨，还剩多少吨没卖完？
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(9/10) - (1/5) - (3/10)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>