A bookstore launched a discount card during the National Day promotion. Each card is priced at 20 yuan, and you can get 20% off when you buy books with the card. Once Mr. Chen bought 20 books worth 8 yuan each for a certain interest group, so how much did Mr. Chen spend on buying books this time?
某书店在国庆促销活动中，推出一种优惠卡，每张卡售价20元，凭卡购书可便宜2折．有一次陈老师为某兴趣小组购买了价值每本8元的图书20本，那么陈老师这次购书共用去多少元？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">8 * 20 * (4/5)</gadget>
<output>128</output>

<gadget id="calculator">128 + 20</gadget>
<output>148</output>

<result>148</result>