A virus-scanning program is checking every file for viruses. It has completed checking 40% of the files in 300 seconds. How long should it take to check all the files
If the time to do it all is T, then
0.4 T = 300
Solve for T.
If you haven't learned algebra yet, think of it this way:
2/5 of the total time is 300.
After 300 seconds, you still need 1 1/2 times as much time as that to finish