A theater can seat 320 people. The number of rows is 4 less than the number of seats in each row. How many rows of seats are there?
回答 (5)
2015-07-12 1:57 am
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2015-07-12 1:53 am
16 rows of 20 seats
2015-07-12 1:51 am
assume there are n seats in each row, then there are n-4 rows in the theatre.
so this is a quadratic equation:
n(n-4)=320
so this is a quadratic equation:
n(n-4)=320
2015-07-12 1:51 am
All the rows have the same number of seats? Then there are 16 rows of 20 seats each.
16 * 20 = 320
16 * 20 = 320
2015-07-12 1:49 am
Let R be the number of rows and S be the number of seats. Then
R = S - 4
Also
RS = 320
Substituting S-4 for R in the first equation
(S - 4)S = 320
S^2 - 4S - 320 = 0
(S - 20)(S + 16) = 0
Since S > 0, S = 20 => R = 16
R = S - 4
Also
RS = 320
Substituting S-4 for R in the first equation
(S - 4)S = 320
S^2 - 4S - 320 = 0
(S - 20)(S + 16) = 0
Since S > 0, S = 20 => R = 16
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