@iambatman @Hero an arithmetic sequence consists of 21 terms. the sum of three terms in the middle is 129, and the last three have a sum of 237. find the series.

Question

tkhunny · Answer

Arithmetic Sequence:

1st term: a
2nd Term: a+r
3rd Term: a+2r
4th Term: a+3r
etc.

"an arithmetic sequence consists of 21 terms."

a + (a+r) + (a+2r) + ... + (a + 20r)

"the sum of three terms in the middle is 129"

Terms 9, 10, and 11

(a+8r) + (a + 9r) + (a+10r) = 129

"last three have a sum of 237"

Terms 19, 20, and 21

(a+18r) + (a + 19r) + (a+20r) = 237

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