Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    1
    ReputationRep:
    These questions will be the death of me

    1. In how many way's can the letters EIGHTEEN be arranged
    2. A group of 5 first year and 3 second year students are having their picture taken standing up in a row:
    i) In how many ways can they stand?
    How many ways can they be arranged if:
    a) all the first years stand together
    b) all the first AND the second years stand together
    c) None of the second years stand next to each other

    Question's sound so damn easy but I really can't figure it out. :<
    Please help ;-; <3
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    These questions will be the death of me

    1. In how many way's can the letters EIGHTEEN be arranged
    2. A group of 5 first year and 3 second year students are having their picture taken standing up in a row:
    i) In how many ways can they stand?
    How many ways can they be arranged if:
    a) all the first years stand together
    b) all the first AND the second years stand together
    c) None of the second years stand next to each other

    Question's sound so damn easy but I really can't figure it out. :<
    Please help ;-; <3
    do you know any formulas about permutations?
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    do you know any formulas about permutations?
    Formulas? Ah, I thought you needed to work them out by using factorial notation... or am I thinking wrong?:confused:
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    Formulas? Ah, I thought you needed to work them out by using factorial notation... or am I thinking wrong?:confused:
    well permutation formulas are factorials, so let me rephrase

    if you have 8 different letters do you know how many 8 letter words, 7 letter words, 6 letter words etc can you make.


    then what do you do if a letter appears twice
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    well permutation formulas are factorials, so let me rephrase

    if you have 8 different letters do you know how many 8 letter words, 7 letter words, 6 letter words etc can you make.


    then what do you do if a letter appears twice
    If the letter appears twice... do you just ignore it? :s Since the question asked 'How many ways can the letters of EIGHTEEN be arranged', I did '6 factorial', but i'm not sure...
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    If the letter appears twice... do you just ignore it? :s Since the question asked 'How many ways can the letters of EIGHTEEN be arranged', I did '6 factorial', but i'm not sure...
    STATISTICS

    10 letters

    S = triple repeat
    T = triple repeat
    I = double repeat

    how many 10 letter words

    10!/(3!3!2!)

    try yours
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    STATISTICS

    10 letters

    S = triple repeat
    T = triple repeat
    I = double repeat

    how many 10 letter words

    10!/(3!3!2!)

    try yours
    8!/3! = 6720 ?
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    8!/3! = 6720 ?
    I think so
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    I think so
    Does the same apply for the other question too?
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    Does the same apply for the other question too?
    not quite

    just permutation modelling based on a handful of themes.
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    not quite

    just permutation modelling based on a handful of themes.
    Ah so I need to answer the second question differently from the first one? :s
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    Ah so I need to answer the second question differently from the first one? :s
    different modelling but you can think of the students like letters
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    different modelling but you can think of the students like letters
    So 5 first years and 3 seconds years would be:
    8!
    ?
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    So 5 first years and 3 seconds years would be:
    8!
    ?
    treat the ones that need to be together as "one letter"
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    treat the ones that need to be together as "one letter"
    Ah! So It's 2! ??
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    Ah! So It's 2! ??
    which part of 2 are you doing?
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    which part of 2 are you doing?
    I'm doing
    2i) How many ways can they stand
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    I'm doing
    2i) How many ways can they stand
    sorry I missed that part

    If there are no restrictions you gave the correct answer in post 13
    • Thread Starter
    Offline

    1
    ReputationRep:
    (Original post by TeeEm)
    sorry I missed that part

    If there are no restrictions you gave the correct answer in post 13
    Ah that's fine ^_^ Hmm so for part a)

    a) all the first years stand together... would that be 5! ?
    Offline

    19
    ReputationRep:
    (Original post by Affection)
    Ah that's fine ^_^ Hmm so for part a)

    a) all the first years stand together... would that be 5! ?
    firstly treat the 1st years as one lump (inseparable) and the 3 2nd years separately.

    work out this perm


    then how many perms can you get from the lump of 5...


    etc
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you rather give up salt or pepper?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.