Question

A stadium has 55,000 seats. Seats sell for ​$28 in Section​ A, ​$16 in Section​ B, and ​$12 in Section C. The number of seats in Section A equals the total number of seats in Sections B and C. Suppose the stadium takes in ​$1,158,000 from each​ sold-out event. How many seats does each section​ hold?

Answer 1

A=number of seats in section A
B=number of seats in section B
C=number of seats in section C

We can suggest this system of equations:

A+B+C=55,000
A=B+C                                      ⇒A-B-C=0
28A+16B+12C=1,158,000

We solve this system of equations by Gauss Method.

1             1              1               55,000
1            -1            -1                         0
28         16           12          1,158,000 


1             1              1               55,000
0            -2             -2             -55,000                                    (R₂-R₁)
0           12             16           382,000                                    (28R₁-R₂) 


1            1                1              55,000
0           -2              -2             -55,000
0            0                4               52,000                                     (6R₂+R₃)

Therefore:

4C=52,000
C=52,000/4
C=13,000


-2B-2(13,000)=-55,000
-2B-26,000=-55,000
-2B=-55,000+26,000
-2B=-29,000
B=-29,000 / -2
B=14,500.

A + 14,500+13,000=55,000
A+27,500=55,000
A=55,000-27,500
A=27,500.

Answer: there are 27,500 seats in section A, 14,500 seats in section B and 13,000 seats in section C.