Creatively image a question and justification for this answer: 400
The question is: 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?
Step-by-step reasoning process: The number of non - valuable files Brennan downloaded in the first round is 70 / 100 * 800 = 560 files. The number of valuable files Brennan downloaded in the first round is 800 - 560 = 240. When he downloaded 400 new files, there were 3 / 5 * 400 = 240 non - useful files, which he deleted again. The total number of valuable files he downloaded in the second round is 400 - 240 = 160. To write his research, Brennan had 160 + 240 = 400 useful files to reference to write his research.