In an AP
Given a = 5, d = 3, an =50, find n and Sn.
Here a = 5, d = 3, an = 50
We know that, an = a + (n – 1 )d
⇒ 50 = 5 + (n – 1) x 3
⇒ 50 – 5 = 3 x (n – 1)
⇒ 45 = 3 x (n – 1)
= 8 x [ 10 + 15 x 3]
= 8 x 10 + 45
= 8 x 55 = 440
Hence, n = 16
and Sn =S16 = 440