Question

The first term of an A.p. is 5 and the Last term is 45.If the sum of all the terms is 400,the number of term is..?​

Answer 1

first term a=5, last term l=45 and Sn = 400

Since, Sn=2n(a+l)

⇒400=2n(5+45)

⇒400=2n(50)

⇒400=n(25)

⇒n=16

Since, l=a+(n−1)d

⇒45=5+(16−1)d

⇒45−5=(15)d

⇒40=15d

⇒d=1540

⇒d=38

HOPE IT HELPS

PLEASE MARK ME BRAINLIEST

THANKYOU