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seniors&freshmen

by pemdas » Sun Feb 05, 2012 3:13 pm
In how many different ways can 5 seniors and 3 freshmen be seated in a row of 8 chairs such that the seniors are not separated, and the freshmen are not separated?

A 360
B 720
C 1440
D 2800
E 3200

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by [email protected] » Sun Feb 05, 2012 4:34 pm
There can be 2 arrangements:
SSSFFFFF
FFFFFSSS
and in each of the above arracgment can be made in 5!x3! ways. So total ways would be=2x360=720.
IMO B
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by pemdas » Sun Feb 05, 2012 4:58 pm
[email protected] wrote:There can be 2 arrangements:
SSSFFFFF
FFFFFSSS
and in each of the above arracgment can be made in 5!x3! ways. So total ways would be=2x360=720.
IMO B
Please explain how you obtained the selection in red?
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by [email protected] » Sun Feb 05, 2012 7:12 pm
pemdas wrote:
[email protected] wrote:There can be 2 arrangements:
SSSFFFFF
FFFFFSSS
and in each of the above arracgment can be made in 5!x3! ways. So total ways would be=2x360=720.
IMO B
Please explain how you obtained the selection in red?
I miscalculated it earlier as per my logic.
5!x3!=120x6=720.
SO total ways would be 720x2=1440.
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by LalaB » Sun Feb 05, 2012 9:31 pm
got the same answer 2!*5!*3!=1440
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by pemdas » Sun Feb 05, 2012 11:25 pm
yes, right
thanks
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