Question
Mathematics Question on Arithmetic Progression
The sum of the first 16 terms of an AP whose first term and the third term are 5 and 15 respectively is
Answer
Explanation:
1st Method1st term =53rd term =15 Then, d=516th term =a+15d=5+15×5=80 Sum =n×(a+l)2= no. of terms × first term + last term 2=16×(5+80)2=16×852=8×85=6802nd Method(Thought Process). Sum = number of terms x average of that APSum=16×(5+80)2=16×852=8×85=680Hence, the correct answer is 680.