Question

in the auditorium there are 24 rows of seats. the first second rows have 8 chairs and the third and fourth rows have 10 chairs.if this pattern continues.how many chairs are in the auditorium?
Since the rows come in pairs, the sequence looks like

8 8 10 10 12 12 ...

SO, considering the nth pair of rows, they have 12+4n seats together.

In 24 rows, there are 12 pairs, so
the 12th pair has 12+48 = 60 seats

the sum is

12/2 (8+60) = 6*68 = 408 seats

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