Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Today is Angelina birthday. She invited four friends to her [#permalink]
01 Feb 2006, 13:56
33% (03:02) correct
67% (00:31) wrong based on 6 sessions
This topic is locked. If you want to discuss this question please re-post it in the respective forum.
Today is Angelina birthday. She invited four friends to her party: Barbara, Carol, Don, and Frank. Everyone will be seated on a round table. How many possible way can these people be seated if Don and Carol must always sit next to each other?
i got 12 too (after some serious thought).
My initial thought was 4! x 2, but because the tabe is circular, you have to realize that ABCDF is the same as BCDFA, so only the combinations of the three other guests matter: 3!, then multipy by 2, for the cases in which CD are switched.
Is there a more mathematical explanation for this, or an analagous real-world situation (the way the electing 3 officers out of 9 people is analagous to creating 3-digit number out of 9 digits)?
ie- what are other expamples of circular permutations that aren't so blatanly worded as "x people sitting in a circle"?