Question

the sum of the first 25 terms of an arithmetic sequence is 350.find is the 13 th term of the sequence?​

Answer 1

Answer:

Multiply 24 times 5 to get 120. Add 120 to -9 to get the 25th term, 111. Now the sum of the 1st term and the 25th term is the same as the sum of the 2nd and the 24th which is the same as the sum of the 3rd and the 23rd, etc., etc., etc. So you will have twelve sums of 102. The sum of those sums is 12 x 102 or 1224. All that is missing is the thirteenth term, which is -9 + 12(5), commonly known as 51. 1224 + 51 = 1275, which is the answer to your question.