Q11 of 110 Page 53

Solve: 1 + 6 + 11 + 16 + ….. + x = 148.

In the A.P.


First term = 1


Common difference = 6 – 1 = 5


Sum of terms =


⇒ 148 =


⇒ 148 =


⇒ 296 = n (5n–3)


⇒ 5n2 – 3n –296 = 0


⇒ 5n2 –40n + 37n –296 = 0


⇒ 5n(n–8) + 37(n–8) = 0


⇒ (n–8)(5n + 37) = 0


⇒ n = 8 or 5n = –37


As negative value of n is not possible, n = 8


⇒ x = 8th term of the series


⇒ x = 1 + (8–1)5


⇒ x = 1 + 35 = 36


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