In a certain city, the coin is 2 yuan each time you take the bus. If you use the bus card, you will be deducted 1.8 yuan each time. How much cheaper is the bus card than the coin?
某市乘坐公交车每次投币2元，如果刷公交卡，则每次扣费1.8元，刷公交卡比投币便宜百分之几？
<gadget id="calculator">2 - 1.8</gadget>
<output>0.2</output>

<gadget id="calculator">0.2 / 2</gadget>
<output>0.1</output>

<result>0.1</result>