During the New Year's Day, the price of Haier's washing machine after a 20% discount is 720 yuan. How much cheaper is it?
元旦期间海尔洗衣机打八折后的售价是720元，便宜了多少元？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">720 / (4/5)</gadget>
<output>900</output>

<gadget id="calculator">900 - 720</gadget>
<output>180</output>

<result>180</result>