On Sunday, my mother bought 5 ice creams and some watermelons from the supermarket, and paid the salesperson 18 yuan in total. Each ice cream is 2 yuan, and each kilogram of watermelon is 1 yuan. How many kilograms of watermelon did mom buy in total?
星期天，妈妈从超市买回5个冰激凌和一些西瓜，共付给售货员18元．每个冰激凌2元，每千克西瓜1元．妈妈一共买了多少千克西瓜？
<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">18 - 10</gadget>
<output>8</output>

<gadget id="calculator">8 / 1</gadget>
<output>8</output>

<result>8</result>