A batch of 800 tons of cement is shipped in. Half (1/2) of the total amount is used on the first day, and 40% of the total amount is used on the second day. How many tons of cement are left?
运来一批800吨水泥，第一天用去了总数的(1/2)，第二天用去了总数的40%，还剩下多少吨水泥？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">800 * (1/10)</gadget>
<output>80</output>

<result>80</result>