Q. An AP consists of 23 terms. If the sum of the three terms in the middle is 141 and the sum of the last three terms is 261, then the first term is
A) 6
B) 5
C) 4
D) 3
Explanation
(d)
$t_{11} + t_{12} + t_{13} = 141$
And $t_{21} + t_{22} + t_{23} = 261$
$\therefore 3a + 33d = 141$
$\Rightarrow a + 11d = 47$ …(i)
And $3a + 63d = 261$
$\Rightarrow a + 21d = 87$ …(ii)
On solving Eqs. (i) and (ii), we get
$a = 3,\ \ d = 4$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.