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Mathematics 67 Online
OpenStudy (anonymous):

In an arithmetic series, the terms of the series are equally spread out. For example, in 1 + 5 + 9 + 13 + 17, consecutive terms are 4 apart. If the first term in an arithmetic series is 3, the last term is 136, and the sum is 1,390, what are the first 3 terms? A. 3, 10, 17 B. 3, 23, 43 C. 3 , 36.333 , 70 D. 3, 69.5, 136 2 E. 3, 139, 1,251

OpenStudy (lgbasallote):

first term is given..last term is given...and sum is given... so use summation formula to get the number of terms \[\huge s_n = \frac{n(a_1 + a_n)}2\] does that help?

OpenStudy (anonymous):

Yes! Thank you very much.

OpenStudy (lgbasallote):

welcome

OpenStudy (anonymous):

wait, What is N??

OpenStudy (anonymous):

the number of terms? would 3 be n in this case?

OpenStudy (anonymous):

You can solve for n using that equation.

OpenStudy (anonymous):

You'll need to find how far apart (the equal spacing) between the terms is.

OpenStudy (anonymous):

Also, since it's multiple choice, you can eliminate some of those answer choices because the terms are not equally spaced.

OpenStudy (lgbasallote):

yes. n is the number of terms. And no, 3 is the first term so it's a1

OpenStudy (lgbasallote):

an is the last term so that would be 136 sn is the sum so that would be 1390

OpenStudy (anonymous):

And n is not 3 just because they are asking for the first 3 terms either.

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