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

    15
    ReputationRep:
    https://cdn.discordapp.com/attachmen...80/unknown.png

    Why are both the numbers 1 and 1? I thought it'd be 2 and 1
    Offline

    1
    ReputationRep:
    enjoy math 😂😂😂😂😂 ..... i dont like math but .....i have 3math books in this semester. .....i study partial differential equations, derivatives, integration ,. so difficult 😰
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by Mr.Rahul Tiwari)
    enjoy math 😂😂😂😂😂 ..... i dont like math but .....i have 3math books in this semester. .....i study partial differential equations, derivatives, integration ,. so difficult 😰
    thank you for your helpful response.
    Offline

    17
    ReputationRep:
    (Original post by will'o'wisp2)
    https://cdn.discordapp.com/attachmen...80/unknown.png

    Why are both the numbers 1 and 1? I thought it'd be 2 and 1
    Consider building a sequence adding up to n+1.

    (1) You can either start with a 1, and follow up with a sequence adding up to n.

    (2) Or you can start with a 2, and follow up with a sequence adding up to n-1.

    How many sequences will work for (1)?
    How many sequences will work for (2)?

    So...?
    Offline

    1
    ReputationRep:
    may I any help you. .......you study in ... which standard .....

    are you from which country
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by DFranklin)
    Consider building a sequence adding up to n+1.

    (1) You can either start with a 1, and follow up with a sequence adding up to n.

    (2) Or you can start with a 2, and follow up with a sequence adding up to n-1.

    How many sequences will work for (1)?
    How many sequences will work for (2)?

    So...?
    n sequences for 1
    and n sequences for 2?
    Offline

    17
    ReputationRep:
    (Original post by will'o'wisp2)
    n sequences for 1
    and n sequences for 2?
    No. Read carefully what I wrote and compare it with how your question defines Xn
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by DFranklin)
    No. Read carefully what I wrote and compare it with how your question defines Xn
    Xn is the number of different sequences of which you can use 1s and 2s to make the number n

    So if you start with a 1 then you can make X1 etc if you start with 2 then you make ??? it doesn't work for X1 but for every sequence after thatbut i still don't understand why it shouldn't be 2,1
    Offline

    17
    ReputationRep:
    Again, look at what I wrote, compare it to the definition of Xn, and then see if you can answer the 2 sub-questions I gave you.
    • Thread Starter
    Offline

    15
    ReputationRep:
    (Original post by DFranklin)
    Again, look at what I wrote, compare it to the definition of Xn, and then see if you can answer the 2 sub-questions I gave you.
    ok, i've had a think and i think you're talking about the terms separately

    so with 1 you work with any combinations of 1 and 2 and make that up to n
    the number of sequences that will work when you start with 1 is n number of sequences as show by Xn where X1=1 and X2=2 etc

    with 2 you can also work with any combo of 1 and 2 to make the n-1 term
    the number of terms you can make when you start with 2 is n-1 because starting with 2 can't ever make X1 but it will make any other Xn provided the n is not 1
    Offline

    17
    ReputationRep:
    After all you've written, it's still not that clear what you're saying are the answers to the 2 questions I asked. I think you're saying the answers are n and n-1 in which case you are wrong (in fact it's clear you are 100% barking up the wrong tree).

    In particular, stop fixating on "if you start with 2 you can't ever make X1", because this is a total red herring that is leading you astray.

    I will ask the first 2 questions again, being even more explicit about what is going on:

    Consider building a sequence adding up to n+1.

    (1) You can either start with a 1, and follow up with a sequence of 1s and 2s which add up to n.

    Now, look at the definition of X_n, and write down how many such sequences there are.

    So, how many possible sequences are there in case (1)?

    (2) You can either start with a 2, and follow up with a sequence of 1s and 2s which add up to n-1.

    Now, look at the definition of X_n, and write down how many such sequences there are.

    So, how many possible sequences are there in case (2)?

    I feel you are still jumping off into your own thoughts rather than answering the questions I am asking you. You should be able to answer all 4 questions (the parts in either bold italic or italic) in considerably less than 40 characters. (And with very little effort or calculation).
 
 
 
  • 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
    Will you be richer or poorer than your parents?
    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

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