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#1 2013-09-05 14:24:32

Ani
Guest

arithmetic series

I've been sitting for a few hours thinking how to figure out the question below, could you help me solve this in a step-by-step format?

The Question;
The sum of the first five terms of an arithmetic series is 85. The sum of the first six terms is 123. What are the first four terms of the series?

Thank you for any help

#2 2013-09-05 15:50:27

Fruityloop
Member
Registered: 2009-05-18
Posts: 120

Re: arithmetic series

Use the difference between the sums to head towards an answer.


The eclipses from Algol (an eclipsing binary star) come further apart in time when the Earth is moving away from Algol and closer together in time when the Earth is moving towards Algol, thereby proving that the speed of light is variable and that Einstein's Special Theory of Relativity is wrong.

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#3 2013-09-05 18:41:25

Ani
Guest

Re: arithmetic series

Thank you smile

#4 2013-09-05 18:42:05

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,311

Re: arithmetic series

hi Ani

Welcome to the forum.

From that information and with subtraction, you can say what the sixth term is.

There are two formulas that can be used:

and

So you can make two simultaneous equations in a and d.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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