Is this correct?

Question

Solve for z:

x = 2.5y

x + y + z = 66

x - 2y - 2z = -12

(A) z = -102

(B) z = 16

(C) z = 10

(D) z = -74

(E) None of the above

For this I got; (C) z = 10. Is this correct?

Answer 1

Yes. Using Cramer's Rule, I get

x = 40

y = 16

z = 10

You can test my answer by plugging these values into the three equations.

Answer 2

Since you are given that that x = 2.5 y, I thought the logical place to start would be to eliminate the z's in the other 2 equations. I multiplied the 2nd equation by 2, added the 2nd and 3rd equations, was left with 3x = 120 so x = 40

Plug that x value into x = 2.5y and you find that y = 16

Take the 40 and 16, plug them in for x & y in the last equation and you'll find that z = 10.

I think you were spot on! Good job. I hope this helped. If you ever want more online tutoring, contact Wyzant.com and they can connect us.

Enjoy the math!

Jetta McGinniss