A thermos cup, the original price is 20 yuan, two stores A and B are now promoting in the following way. Store A: Sell at a 9% discount; Store B: 10% off. According to this, what is the lowest price of this kind of thermos cup now?
一保温杯，原价是20元，甲、乙两个商店现在以下列方式促销．甲店：降价9%出售；乙店：打九折．据此，这种保温杯现在最低价是多少元．
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">20 * (9/10)</gadget>
<output>18</output>

<result>18</result>