Using the timers, they measured various amounts of time in the shortest way possible.
It took 6 minutes to measure 1 minute, 5 minutes to measure 2 minutes, and 3 minutes to measure 3 minutes.
Which 2 timers do they own?
As an example, if you used the 3 and 4 minute timers, the 4 minute timer would have 1 minute left to run when the 3 minute timer finished.
It would take 4 minutes to measure 1 minute.
Try to exclude the timers that can't be used so that you cn narrow down the ones that were.
For example, if it took 6 minutes to measure 1 minute, that means that the 1 minute timer can't have been used as that would have taken just 1 minute in total.
It took 5 minutes to measure 2 minutes.
This would have taken just 2 minutes with the 2 minute timer, which means that this timer can't have been used.
It took 3 minutes to measure 3 minutes.
This would be possible by using the 3 minute timer once or the 1 minute timer 3 times.
We already know the 1 minute timer was not used, so that means the 3 minute timer must have been used here.
If you use the 3 minute timer twice, it takes 6 minutes.
Look at the 4 minute timer and the 5 minute timer and work out which of them would fit in with the details in the question.
The answer is 'C and E'.