Q. 144.2( 5 Votes )

How many three-di

Answer :

To find: 110 + 121 + 132 + ….... + 990


Given,


a = 110


d = 121 – 110 = 11


an = 990


a+(n – 1)d = 990


Therefore,


110 + (n -1) ×11 = 990


(n -1)×11 = 990 – 110 = 880


(n – 1)881/11 = 80


n- 1 = 80


n = 80+1 = 81


As,


Sn = n/2(a1+an)


= 81/2(110+990)


= 81/2(1100) = 81×550 = 44550


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