math
posted by Allen .
Business and finance. Avirus 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 you add another 40%, you will be done with 80% in 600 seconds. 20% is left. .20 times 600=120 sec
600+120=720 sec 
Jen is wrong.
A simple test of taking 40% of her answer of 720, which would be 288, would have indicated it was not right
let the total time be x seconds
so .4x = 300
x = 300/.4 = 750 seconds
(check: 40% of 750 = 300)