Question
A museum offers four video programs that run continously throughout the day, each program starting anew as soon as it is finished. The first program runs every 15 minutes, the second every 30 minutes, the third every 45 minutes, and the fourth every 40 minutes; the first show of each program starts at 10:00 AM and the last showing of each program ends at 4:00 PM. If a tour group can watch the programs in any order, but needs at least ten minutes between programs to regroup, what is the least amount of time the group can take to watch all four programs?

My Question
So for 1st show, times will be: 10:00 / 10:15 / 10:30 / 10:45 / 11:00 etc
2nd show: 10:00 / 10:30 / 11:00 / 11:30 etc.
3rd show: 10:00 / 10:45 / 11:30 / 12:15 / 1:00 etc.
4th show: 10:00 / 10:40 / 11:20 / 12:00 / 12:40 etc.

As an example of the answer, the explanation chose 11:40 - 12:20 for the 4th show. But as far as I can tell, show time should be 11:20 or 12:00, not 11:40.

Please explain where I'm getting this wrong.

Thank you!

This is a typo, and has been noted in the errata:

http://www.manhattangmat.com/errata-wt-4ed.cfm

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Ben Ku
Instructor
ManhattanGMAT

Could somebody please explain above question in easy way? I am completely lost. Please help!

This one was answered recently by Tim: word-trans-4th-ed-ch-8-pg-140-question-9-t10555.html

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Jamie Nelson
ManhattanGMAT Instructor