To prepare 500 grams of medicine for spraying on vegetables, the medicine and water are prepared in a ratio of 3:7, how many grams of medicine are needed?
要配置一种蔬菜地喷洒的药水500克，药和水按3：7的比例配制，需要多少克药？
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

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

<gadget id="calculator">500 * (3/10)</gadget>
<output>150</output>

<result>150</result>