Answer :

To Find: we need to find a number of terms in the given AP.

Given: The series is 11, 18, 25, 32, 39, …. 207

a1=11, a2= 18,d=18–11 = 7 and an=207

(Where a=a1 is first term, a2 is second term, an is nth term and d is common difference of given AP)

Formula Used: an = a + (n–1)d

an= 207 = a1 + (n–1)(7)

207– 11 = (n–1)(7) [subtract 11 on both sides]

196 = (n–1)(7)

28 = (n–1) [Divide both side by 7]

n = 29 [add 1 on both sides]

So there are 29 terms in this AP.

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