BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Permitations and combinations

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 11
Joined: Wed Apr 13, 2011 8:52 pm

Permitations and combinations

by joinn » Wed Jul 06, 2011 1:59 am
The principal of a high school needs to schedule observations of 6 teachers. She
plans to visit one teacher each day for a workweek (Monday through Friday), so she
will only have time to see 5 of the teachers. How many different observation schedules
can she create?

the answer is 6!. how come it is 6!. what is the answer then when the days are six and the days are four.
Top
Source: — Problem Solving |
Legendary Member
Posts: 1448
Joined: Tue May 17, 2011 9:55 am
Location: India
Thanked: 375 times
Followed by:53 members

by Frankenstein » Wed Jul 06, 2011 2:07 am
Hi,
1st day - She can select any of the 6 teachers - 6ways
2nd day - 1 of the remaining 5 - 5ways
3rd day - 1 of the remaining 4 - 4 ways
4th day - 1 of the remaining 3 - 3 ways
5th day - 1 of the remaining 2 - 2 ways

So, total number of ways is 6.5.4.3.2 = 6!(6P5)
If the number of days is 6, then 6.5.4.3.2.1 = 6!
If the number of days is 4, then 6.5.4.3 = 6P4
Cheers!

Things are not what they appear to be... nor are they otherwise
Top
Post new topic Post Reply
• Page 1 of 1