batch of 420 tons of coal is burned (2/7), how many tons are burned?
一批煤420吨，烧去(2/7)，烧去多少吨？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">420 * (2/7)</gadget>
<output>120</output>

<result>120</result>