The price of an LED TV in a shopping mall is 4,000 yuan. Xiaoming’s mother participates in a group purchase online, and it only costs 2,400 yuan. How much cheaper is Xiaoming’s mother buying this TV online than in a shopping mall?
一款LED电视商场标价是4000元，小明妈妈上网参加团购，只需要2400元，小明妈妈上网购买这款电视比商场便宜了百分之几？
<gadget id="calculator">4_000 - 2_400</gadget>
<output>1_600</output>

<gadget id="calculator">1_600 / 4_000</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>