in an arithmetic sequence there is an even number of term's(adsbygoogle = window.adsbygoogle || []).push({});

the sum of terms in the odd places is 440 and the sum of terms in the even places is 520, the last term is bigger than the first term by 156

find how many term's the arithmetic sequence has.

This was from a previous post, but i wanted to figure it out this way.

I tried out this problem, but i can't seem to go ne where with it.

For sum of even numbers

(a+d+a+2d(n-1))*n = 1040<------------ 2an + 2dn^2 -dn = 1040

For sum of odd numbers

(a + a +2d(n-1))*n = 880<-------------- 2an + 2dn^2 - 2dn = 880

solved the two system of equation

dn = 160

N = total number = 2n

Nd = 320

d(N-1) = 156<----------- d = 164

so solve for N using Nd = 320 = 320/164 = 1.95.....

Obviously this is not correct. What did i do wrong here?

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# Homework Help: Arithmetic progression(alternate method)

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