Question

A theatre has $50$ seats in the first row, $48$ seats in the second row, $46$ seats in the third row, and so on in the decreasing pattern. If the theatre has $20$ rows of seats, how many seats are in the theatre?

• A. $1,350$
• B. $1,360$
• C. $1,370$
• D. $620$

Answer 1

The correct option is D $620$

$S_n=50+48+46+......+20terms$
$S_n=\frac{20}{2}[100+19\times (-2\left)\right]S_n=10(100-38)=620$
Total seats $=620$