To mix 20 tons of concrete, the ratio of cement, sand and gravel is 2:3:5, how many tons of sand are needed?
要搅拌20吨的混凝土，水泥、沙子和石子的比是2：3：5，需要沙子多少吨？
<gadget id="calculator">2 + 3 + 5</gadget>
<output>10</output>

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

<gadget id="calculator">20 * (3/10)</gadget>
<output>6</output>

<result>6</result>