QC & Data Int. (#6) Chapter 3, p.46, #10

[escondido]

I get how you cross multiply, but why is it that after you cross multiply, you get Quantity A to equal abc^2, and Quantity B to equal abc? Why can't it be the other way around, depending on which direction you cross-multiply?

I apologize in advance if this question has been posted elsewhere.

[tommywallach]

Hey Escondido,

Cross-multiplication can't be done in 2 ways. All you're doing is multiplying both sides by the denominators. For example:

1/x = 4/y

If we cross-multiply here, we are simply multiplying both sides by x and then by y (or by y and then by x, the order doesn't change the result). So the y ends up on the left side (because the y on the right cancels), and the x ends up on the right side (because the x on the left cancels): y = 4x.

Does that make sense?

-t