Question

If 3 +5+7+9+... upto n terms = 288, then n = ......,select a proper option (a), (b), (c) or (d) from given options so that the statement becomes correct.(All the problems refer to A.P.)
(a) 12
(b) 15
(c) 16
(d) 17

Answer 1

Let Sn be the sum of n terms in an A.P.

Then, Sn=(n/2)*[2a+(n-1)d]

wehre a is the first term,

Sn=288

a=3

d=5-3=7-5=9-7=2 => d=2

288=(n/2)*[6+(n-1)*2]

288*2=n*6 -2n+2n^2

576=4n+2n^2

Dividing the equation by 2,

n^2+2n=288

n^2+2n-288=0

=> n=16 or n=-18

Thereforem n=16.

Therefore and(c)16.

Answer 2

Answer:

option c is correct answer