Explanation

You could list Derek’s activities:

12:30–1:05 load 1
1:05–1:11 unload/reload
1:11–1:46 load 2
1:46–1:52 unload/reload
1:52–2:27 load 3
Etc.

However, completing this rather tedious list all the way up to 6:35pm is not a good expenditure of time on the GRE. A better approach would be to determine how many minutes are available for Derek to do laundry.

From 12:30 to 6:35 is 6 hours and 5 minutes, or 365 minutes.

It takes 41 minutes to do one load of laundry and then switch to the next one (34 + 4 + 2 minutes).

Divide 365 minutes by 41 to get 8.9… So, Derek can definitely do 8 total loads of laundry plus switching time. What about that extra 0.9…? You need to figure out whether Derek can fit in one more laundry load. Importantly, for this last load he needs only 2 extra minutes to unload, since he will not be reloading the machine.

Multiply 8 (the total number of loads Derek can definitely do) by 41 minutes to get 328 minutes. Subtract 328 from the 365 available minutes to get 37 minutes. That is exactly how much time it takes Derek to do one load of laundry (35 minutes) and then unload it (2 minutes). So, Derek can wash and unload 9 total loads of laundry.


Hence option B is correct!
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We need to determine how many loads can be washed in 6 hours and 5 minutes = 6 x 60 + 5 = 365 minutes. Since each load of laundry is 35 + 2 + 4 = 41 minutes (including unloading and reloading), in 365 minutes, we can do 365/41 ≈ 9 loads.

If we can do exactly 9 loads of laundry before 6:35 pm, let’s ignore the first load for now since it doesn’t need to be reloaded. Let’s count the reload plus wash plus unload time as one load of laundry for each of the remaining 8 loads; then it will take 41 x 8 = 328 minutes for these 8 loads, and we have 365 - 328 = 37 minutes for the first load of laundry. Since the first load requires the wash plus unload time, or 35 + 2 = 37 minutes, this perfectly fits the 37 minutes needed for the first load. Therefore, we can do 9 loads of laundry before 6:35pm.

Answer: B
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