Answer:
16
Step-by-step explanation:
First term (t₁) = a = 3, Common difference (d) = 8 - 3 = 5 and last term (tₙ) = 78
78 = 3 + (n - 1)5
⇒ 78 = 3 + 5n - 5
⇒ 78 = -2 +5n
⇒ 78 + 2 = 5n
⇒ 80 = 5n
⇒ n = 16
Therefore, 78 is 16th term of A.P: 3, 8, 13, 18...
