Question

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1.
A theater has 20 rows of seats. If there are 4 seats in the 1st row 12 in the 2nd row, 20 in the 3rd row . How many seats are there in total? Show and explain all work.

Answer 1

Answer:

1,600 seats in the theater

Step-by-step explanation:

well it seems like each row is being increased by 8 seats each time.

we start with 4 seats in the 1st row. 12 in the 2nd. and 20 in the 3rd. I will make a chart showing you how many seats are in each row.

4th row - 28  5th row - 36   6th row - 44   7th row - 52   8th row - 60   9th - 68   10th - 76   11th - 84    12th - 92   13th - 100    14th - 108   15th - 116   16th- 124    17th - 132   18th - 140    19th - 148    20th - 156

if we add these all together you will get 1,600

Answer 2

Answer:

1600 seats

Explanation:

1st row = 4 seats, 2nd row = 12 seats, 3rd row = 20 seats

This is arithmetic progression with first term (a) being 4 and common difference (d) of 8 and total term (n) of 20.

Sum of arithmetic series:

$\sf S_n = \dfrac{n}{2} ( 2a + (n-1)d)$

insert values

$\sf S_{20} = \dfrac{20}{2} ( 2(4) + (20-1)8)$

$\sf S_{20} = 1600$