Which term of the A.P. 3, 8, 13,… is 248 ?
Given A.P is 3, 8, 13,…
Here, a1 = a = 3, a2 = 8
Common difference, d = a2 – a1 = 8 – 3 = 5
We know, an = a + (n – 1)d where a is first term or a1 and d is common difference
∴ an = 3 + (n – 1)5
⇒ an = 3 + 5n – 5
⇒ an = 5n – 2
Now, to find which term of A.P is 248
Put an = 248
∴ 5n – 2 = 248
⇒ 5n = 248 + 2
⇒ 5n = 250
⇒ n = 50
Hence, 50th term of given A.P is 248