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

    10
    ReputationRep:
    I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

    This is the question

    "I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

    I seriously dont understand what the word before implies .

    My steps are like
    A * (1.035)^n-1 < 2A
    n<21.148
    Hence n = 21

    But the acutal answer is 20.15

    I tried the solution bank but didn't find it helpful.

    Thank You
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by MaleVip)
    I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

    This is the question

    "I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

    I seriously dont understand what the word before implies .

    My steps are like
    A * (1.035)^n-1 < 2A
    n<21.148
    Hence n = 21

    But the acutal answer is 20.15

    I tried the solution bank but didn't find it helpful.

    Thank You
    What does n represent in your equation?

    Think about what it means when n = 1, n= 2 etc in your equation.
    Offline

    15
    ReputationRep:
    (Original post by MaleVip)
    I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

    This is the question

    "I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

    I seriously dont understand what the word before implies .

    My steps are like
    A * (1.035)^n-1 < 2A
    n<21.148
    Hence n = 21

    But the acutal answer is 20.15

    I tried the solution bank but didn't find it helpful.

    Thank You
    For this you don't need A *r^(n-1) but A *r(n)
    Think of it this way you invest A and after 1 year you'll have A*1.035 so your method seems correct except the -1 part
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by SeanFM)
    What does n represent in your equation?

    Think about what it means when n = 1, n= 2 etc in your equation.
    n is the number of years


    Posted from TSR Mobile
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by MaleVip)
    n is the number of years


    Posted from TSR Mobile
    Right.. so when n=1, that's one year, what does the left hand side of your equation suggest? (what I am trying to hint at has been given above already)
    • Thread Starter
    Offline

    10
    ReputationRep:
    (Original post by SeanFM)
    Right.. so when n=1, that's one year, what does the left hand side of your equation suggest? (what I am trying to hint at has been given above already)
    Okay i see what you mean.. Kinda..
    But then..


    "Find which term in the progression 3,12,48... Is the first to exceed 1000000?"

    The actual steps for the answer;

    3*(4)^n-1>1000000

    Why isnt it just 3*(4)^n>1000000
    Like before??




    Posted from TSR Mobile
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by MaleVip)
    Okay i see what you mean.. Kinda..
    But then..
    How does this relate to the equation
    Nth term = ar^n-1??


    Posted from TSR Mobile
    So what is the first term? (n=1) and what does that term mean/signify, in the context of the question?

    Hence what number term are you actually looking for, rather than 21? (With your method you don't have to do any extra calculations, just realise what your n's and n=21 means).
 
 
 
  • 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 like to hibernate through the winter months?
    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.