Given that the sum of the first five items of an arithmetic sequence is 120, the sum of the last five items is 180, and the sum of each item is 360, how many items are there in this sequence

And the sum of each item is 360, (a1 + an) * n / 2 = 360, (a1 + an) * n = 720a1 + A2 + a3 + A4 + A5 = 120an + a (n-1) + a (n-2) + a (n-3) + a (n-4) = 180. The arithmetic sequence is known as an + A1 = A2 + a (n-1) =. By adding the two formulas, we can get 5 (a1 + an) = 120 + 180 = 300a1 + an = 60 and substitute (a1 + an) * n = 720 with n = 12

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