Progressions : Sum of terms of an Arithmetic Sequences

Question

The sum of the first and the 9^th of an arithmetic progression is 24. What is the sum of the first nine terms of the progression?

1. 240
2. 216
3. 108
4. 120
   
   

Correct Choice is (3) and Correct Answer is 108

Explanatory Answer

The sum of the first 'n' terms of an AP is , where 'a' is the first term and 'l' is the last term of the series.

In this question, we know that the sum of the first and the last term (ninth term) = 24.

Therefore, the sum of first 9 terms = = 108

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