Item 18 you and your friend are selling tickets to a charity event. you sell 7 adult tickets and 16 student tickets for $120. your friend sells 13 adult tickets and 9 student tickets for $140. what is the cost of a student ticket

  $4

Step-by-step explanation:

The two purchases can be written in terms of the cost of an adult ticket (a) and the cost of a student ticket (s):

  7a +16s = 120 . . . . . . . . price for the first purchase

  13a +9s = 140 . . . . . . . . price for the second purchase

Using Cramer's rule, the value of s can be found as ...

  s = (120·13 -140·7)/(16·13 -9·7) = 580/145 = 4

The cost of a student ticket is $4.

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Comment on Cramer's Rule

Cramer's rule is particularly useful for systems that don't have "nice" numbers that would make substitution or elimination easy methods to use. If you locate the numbers in the equation, you can see the X-patterns that are used to compute the numerator and denominator differences.

The value of a is (16·140 -9·120)/(same denominator) = 1160/145 = 8. I wanted to show you these numbers so you could see the numerator X-pattern for the first variable.

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Of course, graphical methods can be quick and easy, too.

215.92 dollars is the answer