Question

How many seating capacity does a theater with 20 rows has if it contains 15 seats in the first row and each rows has 2 more seats than the row before it?

Answer 1

sn=15+(n-1)2

the 20th row n=20 so the seats are  

15+(20-1)(2)=53 seats

Answer 2

Answer:

n=20 rows

AP=15,17,19,21......

a=15

d=2

S=n/2(2a+d(n-1))

S=20/2(30+2*19)

S=10*(30+38)

S=10*68

S=680

so 680 seats are there

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