A total of 420 kilograms of watermelons and bananas are shipped from the fruit store, and the mass ratio of watermelons and bananas is 5:2. How many kilograms of watermelons are shipped.
水果商店共运来西瓜和香蕉420千克，西瓜和香蕉的质量比是5：2．运来西瓜多少千克．
<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">420 * (5/7)</gadget>
<output>300</output>

<result>300</result>