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struggling wid basic maths_arthematic progression...

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Re: struggling wid basic maths_arthematic progression...

by logitech » Sat Nov 15, 2008 11:59 am
willbeatthegmat wrote:The sum of the 4th and 8th terms of an AP is 24 and the sum of the 6th and 10th terms is 44. Find the first three terms of the AP?
WIKI has a perfect explanation, which you fill find very useful:

https://en.wikipedia.org/wiki/Arithmetic_progression

4th term: a1+3d
8th term: a1+7d

2a1+10d = 24 I

6th term: a1+5d
10th term: a1+9d

2a1+14d=44 II

II - I :

4d=20, d=5 and solve it for a1, you will get a1= -13

a1=-13
a2=-8
a3=-3
LGTCH
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by cramya » Sat Nov 15, 2008 12:05 pm
In an AP

an = a1+ (n-1) d

where a - first term n- number of terms and d-> common difference

Given a4+a8 = 24
a6+a10 = 44

a4 = a1+3d
a8 = a1+7d
a6 = a1+5d
a10 = a1+9d

a1+3d+a1+7d = 24 -> 2a1+10d = 24->a1+5d=12 (1)

a1+5d+a1+9d = 44-> 2a1+14d = 44->a1+7d=22 (2)

Solve for a1 and d from 1 and 2

d=5
a1=-13
a2=a1+d = -13+5 = -8
a3= a1+2d = -13+2(5) = -3


Hope this helps.

Whats the answer given?
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by dmateer25 » Sat Nov 15, 2008 12:07 pm
AP = arithmetic progression

formula for AP is the nth term = a + (n-1)d, where a=first term



4th term: a + (4-1)d = a+3d

8th term: a + (8-1)d = a+7d

a+3d+a+7d=24
2a + 10d = 24
a + 5d = 12 (i)

6th term: a + (6-1)d = a+5d

10th term: a + (10-1)d = a+9d

a+5d+a+9d=44
2a + 14d = 44
a + 7d = 22 (ii)

subtract the first from the second to get:

2d = 10
d=5

substitute d back into either i or ii

a + 7(5) = 22
a = -13


nth term = a + (n-1)d

a2 = -13 + (2-1)5
a2 = -8

a3 = -13 + (3-1)5
a3 = -3

First three terms are -13, -8, -3
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by dmateer25 » Sat Nov 15, 2008 12:08 pm
cramya wrote:In an AP

an = a1+ (n-1) d

where a - first term n- number of terms and d-> common difference

Given a4+a8 = 24
a6+a10 = 44

a4 = a1+3d
a8 = a1+7d
a6 = a1+5d
a10 = a1+9d

a1+3d+a1+7d = 24 -> 2a1+10d = 24->a1+5d=12 (1)

a1+5d+a1+9d = 44-> 2a1+14d = 44->a1+7d=22 (2)

Solve for a1 and d from 1 and 2

d=5
a1=-13
a2=a1+d = -13+5 = -8
a3= a1+2d = -13+2(5) = -3


Hope this helps.

Whats the answer given?
Beat me too it! Nice work cramya and logitech!
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by willbeatthegmat » Sun Nov 16, 2008 11:35 am
ans is -13,-8,-3.....too gud guys..u made it look preety simple
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