Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    Hi, the following question has got me.
    7 people are to be seated in a row. Calculate the number of ways in which this can be done so that 2 particular people A and B always have exactly one of the others between them (note the answer from the book is 1200)
    I just dont know how to get this.
    any help greatly appreatiated
    Offline

    16
    ReputationRep:
    Consider A - B - - - -,. How many ways can this be done?
    Then - A -B - - - etc.
    • Study Helper
    Offline

    0
    ReputationRep:
    Study Helper
    and don't forget B _ A _ _ _ _, _ B _ A _ _ _, etc.
    Offline

    16
    ReputationRep:
    Think of A?B as one unit, then you 5 things to arrange ... do you know how many ways there are for this

    Then double because of B?A

    Then x5 because ? could be 5 different people
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TenOfThem)
    Think of A?B as one unit, then you 5 things to arrange ... do you know how many ways there are for this

    Then double because of B?A

    Then x5 because ? could be 5 different people
    Thanks 10 of them , yours was the best one .
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by BabyMaths)
    and don't forget B _ A _ _ _ _, _ B _ A _ _ _, etc.
    Thanks baby maths - great help
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by Matureb)
    Consider A - B - - - -,. How many ways can this be done?
    Then - A -B - - - etc.
    Thanks for the help matureb
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 6, 2013
Poll
Do you think parents should charge rent?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.