A fountain pen costs 1 yuan and 40 cents. I bought 2 of them and paid 5 yuan. How much should I get back?
一支水笔1元4角，明明买了2支，付了5元钱，应该找回多少元
<gadget id="calculator">2 * 1.4</gadget>
<output>2.8</output>

<gadget id="calculator">5 - 2.8</gadget>
<output>2.2</output>

<result>2.2</result>