Elementary Algebra

Published by Cengage Learning
ISBN 10: 1285194055
ISBN 13: 978-1-28519-405-9

Chapter 8 - Coordinate Geometry and Linear Systems - 8.6 - Elimination-by-Addition Method - Problem Set 8.6 - Page 378: 50


Tennis balls cost 2 dollars and golf balls cost 3 dollars

Work Step by Step

We call x the cost of a tennis ball and y the cost of a golf ball. Thus, we obtain: $ 3x + 2y = 12 $ And $ 6x +3y = 21$ In order to solve this problem, we multiply one or both of the equations by a value that will make one of the variables cancel. We multiply the top equation by -2, and we multiply the bottom equation by 1. Then, we add the two equations to obtain: $-y = -3 \\ y =3 $ We plug in the given value into the top equation and solve for the other variable: $ 3x + 2(3) = 12 \\ 3x = 6 \\ x =2$
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