During the National Day, Zhongnan Shopping Center launched preferential activities. The original price of each bag of "Jieli" washing powder is 4 yuan. Now buy 3 bags and get one free. Aunt Li buys 3 bags at a time. How much is each bag cheaper?
国庆节期间，中南商场开展优惠活动．"洁丽"牌洗衣粉每袋原价4元，现在买3袋送一袋，李阿姨一次买3袋，每袋便宜了多少钱？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">4 * (3/4)</gadget>
<output>3</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<result>1</result>