Question

How to find n and Sn

Answer 1

Given that

a = 5,  d = 3 and an = 50

So we know that

an = a+(n-1)d         [ nth term of AP ]

⇒ 50 = 5+(n-1)3       [ Given ]

⇒ 50 = 5+3n-3

⇒ 50 = 3n+2

⇒ 3n = 48

⇒  n = 16

And

Sn = n/2[a+an]         { Sum of AP ]

⇒ Sn =16/2[5+50}

⇒ Sn = 8(55)

⇒ Sn = 440

Hence number of terms = 16 and sum = 440.