Q. If twice the 11th term of an AP is equal to 7 times its 21st term, then its 25th term is equal to
A) 24
B) 120
C) 0
D) None of these
Explanation
(c)
Since, $2T_{11} = 7T_{21}$
$\Rightarrow 2(a + 10d) = 7(a + 20d)$
$\Rightarrow 2a + 20d = 7a + 140d$
$\Rightarrow a = - 24d$
$\therefore\ T_{25} = - 24d + 24d = 0$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.