Turn on thread page Beta
    • Thread Starter
    Offline

    11
    ReputationRep:
    I am always uncertain when it comes to word problems, especially when it comes to questions that deals with to calculate amount of money in "n".
    Sometimes you are supposed to use the formulae ar^n-1 and sometimes ar^n.
    Is there any trick I can use to figure out what should the value of "n" ?
    Offline

    5
    ReputationRep:
    (Original post by Sayf200)
    I am always uncertain when it comes to word problems, especially when it comes to questions that deals with to calculate amount of money in "n".
    Sometimes you are supposed to use the formulae ar^n-1 and sometimes ar^n.
    Is there any trick I can use to figure out what should the value of "n" ?
    I find it easiest to check with a small number - like after 2 time units. So do it the longhand way and with the formulae and see which gives the right answer.
    Offline

    13
    ReputationRep:
    (Original post by Sayf200)
    I am always uncertain when it comes to word problems, especially when it comes to questions that deals with to calculate amount of money in "n".
    Sometimes you are supposed to use the formulae ar^n-1 and sometimes ar^n.
    Is there any trick I can use to figure out what should the value of "n" ?
    the formula of geometric series is always ar^n-1. can u help me with a question that confused u so I can help?
    Posted on the TSR App. Download from Apple or Google Play
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by brainmaster)
    the formula of geometric series is always ar^n-1. can u help me with a question that confused u so I can help?
    Go ahead
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by ZaraHuss)
    I find it easiest to check with a small number - like after 2 time units. So do it the longhand way and with the formulae and see which gives the right answer.
    Well you couldn't possibly do that in an exam right? I mean you don't the the right answer.......
    Offline

    5
    ReputationRep:
    (Original post by Sayf200)
    Well you couldn't possibly do that in an exam right? I mean you don't the the right answer.......
    What i meant was do a quick check you're using the right one. You can quickly get the answer for after 1 year by the GCSE method and then check with the formula you've used. The correct formula will be right for 1 year as well as the many years you're probably calculating.
    Alternately the reason use ar^(n-1) is that the first time you add interest is the second year, whereas if you include the first year as getting interest then it would be ar^n. This particularly comes up with money when you put the money into the bank before or after they give interest that year.
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by ZaraHuss)
    What i meant was do a quick check you're using the right one. You can quickly get the answer for after 1 year by the GCSE method and then check with the formula you've used. The correct formula will be right for 1 year as well as the many years you're probably calculating.
    Alternately the reason use ar^(n-1) is that the first time you add interest is the second year, whereas if you include the first year as getting interest then it would be ar^n. This particularly comes up with money when you put the money into the bank before or after they give interest that year.
    Aah, that will do for now. Thanks!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 23, 2018
The home of Results and Clearing

2,541

people online now

1,567,000

students helped last year

University open days

  1. Keele University
    General Open Day Undergraduate
    Sun, 19 Aug '18
  2. University of Melbourne
    Open Day Undergraduate
    Sun, 19 Aug '18
  3. Sheffield Hallam University
    City Campus Undergraduate
    Tue, 21 Aug '18
Poll
A-level students - how do you feel about your results?
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.