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?
How many files did Brennan download in the first round? ** The number of non-valuable files Brennan downloaded in the first round is 70/100*800 = <<70/100*800=560>>560 files.
How many files did Brennan download in the first round? ** The number of valuable files Brennan downloaded in the first round is 800-560 = <<800-560=240>>240
How many files did Brennan download in the second round? ** When he downloaded 400 new files, there were 3/5*400= <<3/5*400=240>>240 non-useful files, which he deleted again.
How many files did Brennan download in the second round? ** The total number of valuable files he downloaded in the second round is 400-240 = <<400-240=160>>160
How many files did Brennan have after deleting the unrelated files he downloaded in the second round? ** To write his research, Brennan had 160+240 = <<160+240=400>>400 useful files to reference to write his research.
#### 400