Question

Find the number of terms in the given ap 3,8,
13 ,18.............78

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Answer 1

16

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...