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Question
Which term of the sequence 3, 8, 13, ........ is 78?
Solution
The given sequence is 3, 8, 13, ........
Now,
8 – 3 = 13 – 8 = 5
Hence, the given sequence is an A.P. with first term a = 3 and common difference d = 5.
Let the nth term of the given A.P. be 78.
⇒ 78 = 3 + (n – 1)(5)
⇒ 75 = 5n – 5
⇒ 5n = 80
⇒ n = 16
Thus, the 16th term of the given sequence is 78.
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