Q4 of 105 Page 139

Which term of the AP : 3, 8, 13, 18, ….. , is 78

Given first term (a) = 3

Common difference (d) = n2-n1 = 8-3 = 5


an = 78


⇒ an = a + (n-1)d


78 = 3 +(n-1) 5


75 = (n-1) 5


(n-1) = 15


n = 16


Therefore 78 is 16th term of the series.


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