Question

In a theater, there are 20 chairs in the first row, each row has 4 more chairs than the previous row, and there are 15 rows. How many chairs are there in the theater?

Answer 1

There are a total of 720 chairs in the theater

Explanation:

First row = 20 chairs

Second row = 24 chairs

Third row = 28 chairs

The given is an arithmetic progression (A.P)

First term

a = 20

Common difference

d = 4

Number of terms

n=15

Sum of the chairs in the theater with a total of 15 rows

Sum of an A.P = n/2 { 2a + (n-1) d}

= 15/2{ 2*20 + (15-1) 4}

= 7.5 { 40 + (14) 4 }

= 7.5 { 40 + 56}

= 7.5(96)

=720 chairs