find the sum of all two digit positive odd natural numbers.(lik: 11,13,15...99) AN A.P. SUM.
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First we will count the number by finding out position of last number
Tn = 11+(n-1)2
99-11 = (n-1)2
88/2 = n-1
45 = n
Last number's position is 45
Sn = 45/2*(88+22)
= 45*55
= 2475
Tn = 11+(n-1)2
99-11 = (n-1)2
88/2 = n-1
45 = n
Last number's position is 45
Sn = 45/2*(88+22)
= 45*55
= 2475
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