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Algebra / Systems of two linear equations in two variables Difficulty: Hard

5 y = 10 x + 11

- 5 y = 5 x - 21

The solution to the given system of equations is x,y. What is the value of 30 x ?

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Explanation

The correct answer is 20 . Adding the first equation to the second equation in the given system yields 5y-5y=10x+5x+11-21, or 0=15x-10. Adding 10 to both sides of this equation yields 10=15x. Multiplying both sides of this equation by 2 yields 20=30x. Therefore, the value of 30 x is 20 .