The first and the last term of A.P. are 7 and 630 respectively. If the common difference is 7, how many terms are there and what is their sum?
Correct Answer: Option(a)
Solution: Given that, a1=7; last term =l=630,d=7 We know that, last term, 1=a+(n−1)d ⇒630=7+(n−1)7 ⇒630=7+7n−7 ⇒7630=n ⇒n=90 We know Sn=2n [First term + Last term] =290[7+630] =45 Thus Sn=28,665