Q. 64.7( 6 Votes )

The first and the

Answer :

Given that, first term = a = 5

Last term = l = 45


To find: common difference (d)


We know that sum of n terms of an AP = n (a + l)/2.


But given, sum of all terms = 400


n (a + l)/2 = 400


n (5 + 45)/2 = 400


n (50)/2 = 400


25n = 400


n = 400/25


n = 16 … (1)


We know that l = a + (n – 1) d.


Substituting the given values and n from (1), we get


45 = 5 + (16 – 1) d


45 = 5 + 15d


45 – 5 = 15d


40 = 15d


d = 40/15


d = 8/3


Ans. The common difference d is 8/3.


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