The new batch of milk in the Sound and Light Supermarket sells 2/5 of the total on the first day and 1/3 of the total on the second day. The difference between the sales of the two days is just 300 boxes. How many cartons are there in this batch of milk? (solution by equation)
声光超市新进一批牛奶，第一天卖出总数的(2/5)，第二天卖出总数的(1/3)，两天的销量刚好相差300箱．这批牛奶共有多少箱？(用方程解)
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(2/5) - (1/3)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">300 / (1/15)</gadget>
<output>4_500</output>

<result>4_500</result>