Question

In a theatre, there are 20 seats in the front row and 30 rows were allotted. Each successive row contains two additional seats than its front row. How many seats are there in the last row?

Answer 1

t₁ = a = 20

t₂ = a + 2 = 22

t₃ = a + 2 + 2 = 24 ⇒ d = 2

∴ There are 30 rows.

t₃₀ = a + 29d

= 20 + 29 × 2

= 20 + 58

= 78

∴ There will be 78 seats in the last row.