David Gwyn J. answered 11/24/20
Highly Experienced Tutor (Oxbridge graduate and former tech CEO)
This question gives you simultaneous equations in two unknown variables Adult tickets, and Child tickets.
theater sells adult tickets for $12 and child tickets for $5 earning a total revenue of $1,160
(1) 12A + 5C = 1160
theater sold 120 tickets for yesterday's matinee
(2) A + C = 120
METHOD 1: you can rearrange (2) so that A = 120 - C then substitute this for A in (1).
Hence 12(120 - C) + 5C = 1160
=> 1440 - 12C + 5C = 1160
=> -7C = 1160 - 1440 = -280
=> C = -280/-7 = 40
Then substitute C in (2) to get A + 40 = 120 => A = 80
METHOD 2: you can multiply (2) by 5 to get 5C and then subtract from (1) to eliminate C term...
12A + 5C = 1160
-
5A + 5C = 600
=
7A + 0C = 560
=> A = 560/7 = 80
now substitute A in (2) to get 80 + C = 120 => C = 40
Hence the theater sold 40 children's tickets and 80 adult tickets.
It's quick to double check: 80 x 12 + 40 x 5 = 960 + 200 = 1160 as required.