Wang Fei's father bought (8/10) tons of briquettes, and burned briquettes in one month (4/5), among which briquettes were burned in the first half of the month (3/10), how many tons of briquettes were burned in the second half of the month?
王飞的爸爸买了(8/10)吨煤球，一个月烧了煤球的(4/5)，其中上半月烧了煤球的(3/10)，下半月烧了多少吨煤球？
<gadget id="calculator">8 / 10</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">(4/5) - (3/10)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(4/5) * (1/2)</gadget>
<output>2/5 = around 0.4</output>

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