Brennan was researching his school project and had to download files from the internet to his computer to use for reference. After downloading 800 files, he deleted 70% of them because they were not helpful. He downloaded 400 more files but again realized that 3/5 of them were irrelevant. How many valuable files was he left with after deleting the unrelated files he downloaded in the second round?
The number of non-valuable files Brennan downloaded in the first round is 70/100*800 = 
<gadget id="calculator">70/100*800</gadget>
<output>560</output>
560 files.
The number of valuable files Brennan downloaded in the first round is 800-560 = 
<gadget id="calculator">800-560</gadget>
<output>240</output>
240.
When he downloaded 400 new files, there were 3/5*400= 
<gadget id="calculator">3/5*400</gadget>
<output>240</output>
240 non-useful files, which he deleted again.
The total number of valuable files he downloaded in the second round is 400-240 = 
<gadget id="calculator">400-240</gadget>
<output>160</output>
160.
To write his research, Brennan had 160+240 = 
<gadget id="calculator">160+240</gadget>
<output>400</output>
400 useful files to reference to write his research.

<result>400</result>