The cafeteria originally had 500 kilograms of flour. After eating bag a, each bag is 80 kilograms. How many kilograms are left?
食堂原有500千克面粉，吃掉a袋，每袋80千克，还剩多少千克．
<gadget id="calculator">500 - 80</gadget>
<output>420</output>

<result>420</result>