Q5 of 85 Page 104

The first term of finite A.P. is 5, the last term is 45 and the sum is 500. Find the number of terms.

Formula used.


Sn = [a + l]


⇒ Sn = 500


⇒ a = 5


⇒ l = 45


Sn = [a + l]


500 = [5 + 45]


500×2 = n×50


n = = 20


∴ Number of terms to get sum 500 is 20


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