An exercise book costs 0.8 yuan, and Xiaodong buys two exercise books for 2 yuan, how much money is left.
一个练习本0.8元钱，小东拿2元钱买两个练习本，还剩多少元钱．
<gadget id="calculator">0.8 * 2</gadget>
<output>1.6</output>

<gadget id="calculator">2 - 1.6</gadget>
<output>0.4</output>

<result>0.4</result>