In a hall the first row has 20 seats and every following row has 2 seats more than the row in front of it. If there are 30 rows, the total number of seats is:

Question

Accepted Answer

1470. The seat counts form an arithmetic progression with a = 20, d = 2 and n = 30. S₃₀ = 30/2 [2(20) + 29(2)] = 15(40 + 58) = 15 × 98 = 1470. (The last row has 20 + 29 × 2 = 78 seats.)

In a hall the first row has 20 seats and every following row has 2 seats more than the row in front of it. If there are 30 rows, the total number of seats is:

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