An alloy is formed by melting and casting zinc and copper in a mass ratio of 2:5. How many tons of zinc are needed to produce 1400 tons of this alloy?
一种合金是由锌和铜按2：5的质量比熔铸而成．生产这种合金1400吨，需要锌多少吨．
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1_400 * (2/7)</gadget>
<output>400</output>

<result>400</result>