Big Ideas Math: Modeling Real Life, Grade 8
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2. Solving Systems of Linear Equations by Substitution
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Exercise 17 Page 210

Practice makes perfect
We want to create a system of linear equations to represent the earnings of a drama club from a production. Let's use x to represent the price of an adult ticket and y to represent the price of a student ticket. From the exercise we know that an adult ticket costs twice as much as a student ticket. x=2 y We also know that the club earned a total of $ 1040 by selling 64 adult tickets at price x and 132 student tickets at price y. 64* x+ 132 * y= 1040 Now we can create a system of equations by combining the two equations we created. x=2y & (I) 64x+132y=1040 & (II)
We want to know how much each ticket costs. We can find this out if we solve the system of equations we created in Part A. x=2y & (I) 64x+132y=1040 & (II) We will use the Substitution Method to solve the system. Notice that Equation (I) is already solved for x. Because of this, we will substitute 2y for x in Equation (II) and solve it for y. Let's do it!

64x+132y=1040
64( 2y)+132y=1040
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Solve for y
128y+132y=1040
260y=1040
y=4

Now that we have a value for y, we can substitute its value for y in either equation and solve for x. Let's substitute 4 for y in Equation (I) for simplicity.

x=2y
x=2( 4)
x=8

We found that an adult ticket costs $ 8 and a student ticket costs $ 4.