One kind of milk costs 1.1 yuan per bag. Xiaohua’s family orders 1 bag of milk every day in April, and pays a total of 28.5 yuan based on the wholesale price. How much cheaper is this per bag than the retail price?
一种牛奶每袋1.1元，小华家四月份每天预订1袋牛奶，按批发价，共付28.5元．这样每袋比零售价便宜多少元？
<gadget id="calculator">28.5 / 30</gadget>
<output>0.95</output>

<gadget id="calculator">1.1 - 0.95</gadget>
<output>0.15</output>

<result>0.15</result>