Question 213039: Each of the rows in the auditorium has two more seats than the row in front of it. If the first row has 21 seats, and there are 40 rows of seats, how many seats are in the last row? How many total seats are there in the auditorium?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Each of the rows in the auditorium has two more seats than the row in front of it. If the first row has 21 seats, and there are 40 rows of seats, how many seats are in the last row? How many total seats are there in the auditorium?
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1st row 21
2nd row 21+1*2
3rd row 21+2*2
4th row 21+3*2
...
40th row 21+39*2 = 99
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Aritmetic series with A = 21, L = 99, d = 2
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S(n) = (n/2)(A+L)
S(40) = (40/2)(21+99) = 20*120 = 2400
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Cheers,
Stan H.
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