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At a local Brownsville play production, 420 tickets were sold.
The ticket prices varied on the seating arrangements and cost $8, $10, or $12.
The total income from ticket sales reached $3920.
If the combined number of $8 and $10 priced tickets sold was 5 times the number of $12 tickets sold,
how many tickets of each type were sold?
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Let x be the number of the $8 tickets, and
let y be the number of the $10 tickets.
Then, from the condition, the number (x+y) is 5/6 of 420, i.e. x+y = 350,
and the number of those who bought the $12 tickets was the rest 1/6 of 420, i.e. 70 persons.
Now we have the system of 2 (two) equations in two unknowns
x + y = 350 (1)
8x + 10y + 12*70 = 3920 (2) (total revenue)
We simplify this system to this EQUIVALENT strandard form
x + y = 350 (3)
8x + 10y = 3080 (4)
Multiply equation (3) by 10 (both sides) and then subtract from it equation (4). You will get then
10x - 8x = 3500 - 3080
2x = 420
x = 420/2 = 210.
Thus 210 persons bought $8 tickets; hence, 350-210 = 140 bought $10 tickets; and the rest 70 persons bought $12 tickets.
Solved.
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By the way, the problem' setup, presented in the post by @josgarithmetic,
IS TOTALLY WRONG,
so for your safety, you better ignore it . . .