The important question from arithmetic progressions of ncert of exercise 5.2 of math. How i solve this question in easy way. It is very important for class 10th board exam Which term of the A.P. 3, 8, 13, 18, … is 78?
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Given the A.P. series as3, 8, 13, 18, …
First term, a = 3
Common difference, d = a2 − a1 = 8 − 3 = 5
Let the nth term of given A.P. be 78. Now as we know,
an = a+(n−1)d
Therefore,
78 = 3+(n −1)5
75 = (n−1)5
(n−1) = 15
n = 16
Hence, 16th term of this A.P. is 78.