Mom bought 2.5 kilograms of beans in the morning market, handed it to the vendor for 20 yuan, and got back 2.5 yuan, how much is it per kilogram of beans.
妈妈在早市上买了2.5千克豆角，交给商贩20元后，找回2.5元，每千克豆角多少元．
<gadget id="calculator">20 - 2.5</gadget>
<output>17.5</output>

<gadget id="calculator">17.5 / 2.5</gadget>
<output>7</output>

<result>7</result>