Answer: Option D Answer: (d)Series of all natural numbers from 75 to 97 is in A.P. whose first term, a = 75, last term, l = 97 If number of terms be n, then $a_n$ = a + (n–1)d97 = 75 + (n – 1) n = 97 – 74 = 23$S_n = n/2(a+l)$$S_23 = 23/2(75+97)$= $23/2$× 172=1978
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