Mary H. answered 02/11/18
Tutor
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Hi Michael
For this problem, we are looking at two different kinds of information : the number of each kind of ticket sold, and the amount of money made on each ticket sold.
First, let x= the number of floor seats sold
y= the number of balcony seats sold
The total number of seats sold is 900, so
x + y = 900
That is your first equation. Now let's think about making money selling tickets. You have to multiply the number bought by the price per item to get the total. Floor seats cost $12 each, so the amount they made selling floor seats is 12x. Balcony seats cost $10 each, so the amount they made selling balcony seats is 10 y. The total they made is 9780.
12x + 10y = 9780
x + y = 900 This looks good for substitution method.
y = 900 - x
12x + 10(900 - x) = 9780
12x + 9000 - 10 x = 9780
2x + 9000 = 9780
2x = 780
x = 390
y = 900 - 390 = 510
CHECK: 12 (390) +10 (510) = 9780