Hi, it is simple arithmetic series sum. The values are not 24 and 25, those are 24 and -25 (minus 25). So, the answer is 24.

Salahuddin

Maths online

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- Oct 26th 2012, 07:04 AM #1

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## sorry asking the same question

Hello friends ,

I am solving this question:

The sum of how may tersm of the series 6 + 12 + 18 + 24 + ... is 1800 ?

where I came across this equation n^2+n-600=0

got the values n=24 or n=25

but i dident understood how to put these values in the eqn as the answer is

ie sum of the terms = only 24

and the question is

sum of how may tersm of the series 6 + 12 + 18 + 24 + ... is 1800?

so how to calcullare sum of the terms ?

so please help me

thanks..............

- Oct 26th 2012, 07:20 AM #2

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## Re: sorry asking the same question

Hi, it is simple arithmetic series sum. The values are not 24 and 25, those are 24 and -25 (minus 25). So, the answer is 24.

Salahuddin

Maths online

- Oct 26th 2012, 08:11 AM #3
## Re: sorry asking the same question

An arithmetic sequence can always be written as

Where is the first term and is the common difference.

So the sequence has the form

So to find out how many terms are in the sequence set

The sum of the first terms of an arithmetic sequence is given by

Now just plug everything in.

Also note that

Using the formula for the sum of the first n integers