in an arithmetic sequence there is an even number of term's 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?