Question

Let $a_1=8, a_2, a_3, \ldots, a_n$ be an AP If the sum of its first four terms is $50$ and the sum of its last four terms is $170$ , then the product of its middle two terms is______

Answer 1

The correct answer is 754.
a1​+a2​+a3​+a4​=50
⇒32+6d=50
⇒d=3
and, an−3​+an−2​+an−1​+an​=170
⇒32+(4n−10)⋅3=170
⇒n=14
a7​=26,a8​=29
⇒a7​⋅a8​=754