Arithmetic Sequence problem(s)..

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kashewman: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Mon Aug 14, 2006 10:52 am; Location: Washington D.C.

by kashewman » Mon Dec 04, 2006 7:28 am

Hey all,

I consistently get sequence problems wrong, is there an easy fix? One problem I recently missed..

In the arithmetic sequence t(1) [all numbers are 'under' the t not an exponent], t(2),t(3)...t(n).., t(1) = 23 and t(n) = t(n-1) - 3 for each n>1. What is the value of n when t(n) = -4?

Any help is apprecaited, thanks!

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Source: Beat The GMAT — Quantitative Reasoning | Mon Dec 04, 2006 7:28 am

kulksnikhil: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Tue May 23, 2006 3:35 pm; Location: Seoul, Korea; Thanked: 2 times

Re: Arithmetic Sequence problem(s)..

by kulksnikhil » Wed Dec 06, 2006 12:19 am

kashewman wrote:Hey all,

I consistently get sequence problems wrong, is there an easy fix? One problem I recently missed..

In the arithmetic sequence t(1) [all numbers are 'under' the t not an exponent], t(2),t(3)...t(n).., t(1) = 23 and t(n) = t(n-1) - 3 for each n>1. What is the value of n when t(n) = -4?

Any help is apprecaited, thanks!

You can easily solve this by going step by step, pluging in previous ( t(n-1) ) value

we know,
t(1) = 23
t(2) = t(1) - 3 = 20
t(3) = 17
4 = 14
5 = 11
6 = 8
7 = 5
8 = 2
9 = -1
10 = -4

However there are Two Arithment Progression equations you may use them, whenever you come across Arithmetic progression Problems..

in a sequence of number

a, a+d, a+2d..... l (where l is the last number)

Last number of the sequence is determined using following equation

Last number l = a + (n-1)d

And sum of all the numbers in the sequence can be determined using the following equation

SUM = (n/2)(2a + (n-1)d)

WHERE
n = number of numbers in the sequence
a = first number in the sequence
l = last numbr in the sequence
d = common difference

generally.. you will have 3 of these values and will be asked the fourth one and SUM Or sum will be given and asked to find n or something like that.

Hope this helps!!

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

quick suggestion to sequence

by resilient » Fri Apr 25, 2008 12:23 pm

I just figured these out and needed to have someone show me how to do it.

The key to success with these is to understand what is happening in the sequence and ten figure out where you stand and then just plug in the numbers in th esequence in order to come to the answer. The explanation in from the writer above did the exact same way I would approach the situation

Appetite for 700 and I scraped my plate!

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rbansal: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Tue Jul 20, 2010 7:42 pmFollowed by: 1 member; Thanked: 1 times

by rbansal » Sat May 07, 2011 11:52 am

kulksnikhil wrote:
kashewman wrote:Hey all,

I consistently get sequence problems wrong, is there an easy fix? One problem I recently missed..

In the arithmetic sequence t(1) [all numbers are 'under' the t not an exponent], t(2),t(3)...t(n).., t(1) = 23 and t(n) = t(n-1) - 3 for each n>1. What is the value of n when t(n) = -4?

Any help is apprecaited, thanks!
You can easily solve this by going step by step, pluging in previous ( t(n-1) ) value

we know,
t(1) = 23
t(2) = t(1) - 3 = 20
t(3) = 17
4 = 14
5 = 11
6 = 8
7 = 5
8 = 2
9 = -1
10 = -4

However there are Two Arithment Progression equations you may use them, whenever you come across Arithmetic progression Problems..

in a sequence of number

a, a+d, a+2d..... l (where l is the last number)

Last number of the sequence is determined using following equation

Last number l = a + (n-1)d

And sum of all the numbers in the sequence can be determined using the following equation

SUM = (n/2)(2a + (n-1)d)

WHERE
n = number of numbers in the sequence
a = first number in the sequence
l = last numbr in the sequence
d = common difference

generally.. you will have 3 of these values and will be asked the fourth one and SUM Or sum will be given and asked to find n or something like that.

Hope this helps!!

How Can we use these equations for the question above I am getting confused?

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