Q7 of 110 Page 53

In the arithmetic sequence 60, 56, 52, 48,…, starting from the first term, how many terms are needed so that their sum is 368?

In the A.P.


First term = 60


Common difference = 56 – 60 = –4


Sum of terms =


⇒ 368 =


⇒ 368 =


⇒ 736 = n (124 – 4n)


⇒ 4n2 – 124n + 736 = 0


⇒ 4n2 – 92n–32n + 736 = 0


⇒ 4n(n–23) –32(n–23) = 0


⇒ (4n–32)(n–23) = 0


⇒ 4n = 32 or n = 23


⇒ n = 8 or n = 23


Therefore, no. of terms can be 8 or 23


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