To prepare a liquid medicine, the ratio of powder to kilograms of water is 1:500. There are 1500 kilograms of existing water, how many kilograms of medicinal powder are needed to prepare this liquid medicine?
配制一种药水，药粉和水的千克数的比是1：500．现有水1500千克，要配制这种药水需药粉多少千克？
<gadget id="calculator">500 / 1</gadget>
<output>500</output>

<gadget id="calculator">1_500 / 500</gadget>
<output>3</output>

<result>3</result>