A concert hall has a total of $20$ rows of seats. ... | Free GMAT Practice Question | GMAT Panda

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A concert hall has a total of 20 rows of seats. The first row has 18 seats and the second row has 21 seats. Each subsequent row has 3 more seats than the previous row. What is the total number of seats in the hall?

Explanation	Calculations	Help
$We first determine how many rows there are from the "second row" to the "twentieth row", inclusive, using the Counting Evenly Spaced Integers Rule .$	$20 - 2 + 1 = 19$	Theory & Tactics Method Card EVEN1-B Click to view full details
$We then find the number of seats in the twentieth row by adding the extra seats that come from each increment of 3 to the second row.$	$21 + 18 \times 3 = 75$
$We then find the total seats from the second through the twentieth row by multiplying the average number of seats by the number of rows using the Sum of Evenly Spaced Integers Rule .$	$\frac{19}{2} \times (21 + 75) = \frac{19}{2} \times 96 = 19 \times 48 = 912$	Theory & Tactics Method Card EVEN1-D Click to view full details
$We add the seats in the first row to this sum to get the total seats in the hall.$	$18 + 912 = 930$

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C

A concert hall has a total of 20 rows of seats. The first row has 18 seats and the second row has 21 seats. Each subsequent row has 3 more seats than the previous row. What is the total number of seats in the hall?

Explanation	Calculations	Help
$We first determine how many rows there are from the "second row" to the "twentieth row", inclusive, using the Counting Evenly Spaced Integers Rule .$	$20 - 2 + 1 = 19$	Theory & Tactics Method Card EVEN1-B Click to view full details
$We then find the number of seats in the twentieth row by adding the extra seats that come from each increment of 3 to the second row.$	$21 + 18 \times 3 = 75$
$We then find the total seats from the second through the twentieth row by multiplying the average number of seats by the number of rows using the Sum of Evenly Spaced Integers Rule .$	$\frac{19}{2} \times (21 + 75) = \frac{19}{2} \times 96 = 19 \times 48 = 912$	Theory & Tactics Method Card EVEN1-D Click to view full details
$We add the seats in the first row to this sum to get the total seats in the hall.$	$18 + 912 = 930$

Scroll horizontally to view all columns

C