This question is from Ncert Book class 10th Ch. number 5 Ex. 5.2 Q. 4 . In the following question you have to find out which term of the A.P given above will be 78. Also give the full solution of the question.
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Solution:
A.P is given as 3, 8, 13, 18, …
a = 3
d = a2 − a1 = 8 − 3 = 5
Let the nth term of the A.P. be 78.
We know,
an = a+(n−1)d
Then,
78 = 3+(n −1)5
75 = (n−1)5
(n−1) = 15
n = 16
The 16th term of this A.P is 78.