Q5 of 105 Page 139

Find the number of terms in each of the following APs :

18, 15, 13 …. , -47

Given first term (a) = 18

Common difference (d) = n2-n1 = 15 - 18 = 2.5


an = -47


⇒ an = a + (n-1)d


-47 = 18 +(n-1) 2.5


65 = (n-1) 2.5


(n-1) = 26


n = 27


Therefore -47 is 27th term of the series


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