An alloy contains copper and iron in a mass ratio of 2:5. If 140 tons of this alloy are produced, the mass of copper required is how many tons less than the mass of iron.
一种合金含有铜、铁的质量比为2：5，若生产这种合金140吨，则需要的铜的质量比铁的质量少多少吨．
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">140 * (3/7)</gadget>
<output>60</output>

<result>60</result>