The supermarket is running promotional activities, each bag of milk powder is 10 yuan, buy 4 bags and get one free, Aunt Wang bought 4 bags at a time, how much cheaper can each bag of milk powder be?
超市搞促销活动，每袋奶粉10元，买4袋送一袋，王阿姨一次买了4袋，每袋奶粉可以便宜多少钱？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">10 * (4/5)</gadget>
<output>8</output>

<gadget id="calculator">10 - 8</gadget>
<output>2</output>

<result>2</result>