Q9 of 176 Page 8

Find the number of terms of the A.P.

7, 11, 15, ..., 139?

Here, a = 7 , d = 11 – 7 = 4 and l = 139


where l = a + (n – 1)d


⇒ 139 = 7 + (n – 1)(4)


⇒ 139 = 7 + 4n – 4


⇒ 139 = 3 + 4n


⇒ 139 – 3 = 4n


⇒ 136 = 4n



Hence, the number of terms in the given AP is 34


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