Question

At the movie theater, child admission is $6.70 and adult admission is $9.90. On Monday, 175 tickets were sold for a total sales of $1476.50.How many adult tickets were sold that day?

Answer 1

Let a be the number of adult tickets sold. Similarly, let c be the number of child tickets sold. Ultimately, we will have a system of equations since there are two unknowns.
We know the total sales were 707.70:
6.10c + 9.20a = 707.70
We also know that a = 3c since there were 3 times as many adult tickets as children tickets. This is all we need.
Substitute a=3c into the first equation.
6.10c + 9.20(3c) = 707.70

6.10c + 27.60c = 707.70
33.70c = 707.70
c = 21 <---- Answer
Extra:
Now let's say that they wanted to know how many adult tickets were sold.
We would plug in c =21 into a =3c to find that 63 ADULT TICKETS were sold.
Hope this helped!