Xiao Ming learned in the store that he bought crystal pens for 1 yuan per plant. If he bought more than 10 plants, it would be calculated at 80 cents per plant. If Xiao Ming bought 20 plants, how much did he spend less?
小明在商店了解到零买水晶笔1元钱1株，如果买10株以上按每株8角钱算，小明买了20株，他少花了多少钱？
<gadget id="calculator">1 - 0.8</gadget>
<output>0.2</output>

<gadget id="calculator">0.2 * 20</gadget>
<output>4</output>

<result>4</result>