Solve.
-A local civic theater has 22 seats in the first row and 21 rows in all. Each successive row contains 3additional seats. How many seats are in the civic theater?
A)1092 seats
B)790 seats
C)1070 seats
D)1010 seats

Question

Quizplus · Accepted Answer

The number of seats forms an arithmetic sequence with the first term $a_1 = 22$, common difference $d = 3$, and number of terms $n = 21$. The sum of an arithmetic series is given by $S_n = \frac{n}{2}[2a_1 + (n-1)d]$. Substituting the given values, $S_{21} = \frac{21}{2}[2(22) + (21-1)3] = \frac{21}{2}[44 + 60] = \frac{21}{2} \times 104 = 21 \times 52 = 1092$ seats.

Solve. -A Local Civic Theater Has 22 Seats in the First