Question

(iii) There are 25 rows of seats in an auditorium. The 1st row is of 20 seats, the 2nd.
row of 22 seats, the 3rd row of 24 seats and so on. How many seats are there
in the 21st row?​

Answer 1

Step-by-step explanation:

According to question . - 1st have 20 seat

2nd have 22 seat

3rd have 34 seat and so on

so it is direct propotion

==> XY1 = YX1

1 * 22 = 21x

22 = 21x

x = 22 * 21 = 462

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Answer 2

The number of seats will be in the following order-  

20, 22, 24,.........

It clearly forms an arithmetic sequence.

From the question, you have

a= 20 (first term), d= 2 (common diff)  

n=21 (asked) , t21=?

The formula of general term is

tn = a+(n-1)d

t21 = 20+(21-1)2

= 20+ (20)2

= 20+40

= 60.

Hope I helped you!