There is a batch of materials to be transported to the disaster area. 40% of the total amount was transported on the first day, and 30% of the total amount was transported on the second day. It is known that a total of 280 tons were transported in two days. How many tons are there in total for this batch of materials?
有一批物质要运往灾区，第一天运走了总数的40%，第二天运走了总数的30%，已知两天共运走了280吨，这批物质共有多少吨？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) + (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">280 / (7/10)</gadget>
<output>400</output>

<result>400</result>