Question

ciniplex has 13 rows of seats with 10 seats in the first row, 12 in the second, 14 in the third row and so on, What is the total number of seats in the ciniplex. 

a) 252

b) 256

c) 258

d) 286


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Answer 1

In this question we have to find out the sum of this AP with d = 2 and A = 10.

Sn = n/2 (a + l)

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

S 13 = 13/2 (20 + (12)2) = 13 * 22 = 286 seats

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