Question

Joanie believes that you cannot use cross products to solve the proportion 50 / 3 equals 75 over x 4x she says that if you multiply both sides of the equation by X you get 50 x / 3 equals 75 then if you multiply both sides of the equation by 3 you get 50 x equals 75 which is a different equation then you would get if you cross multiply what mistake did Yuri make in her reasoning?

Answer 1

The proportion is shown below and we cross multiply, do algebra, to solve it.

$\begin{gathered} \frac{50}{3}=\frac{75}{x} \\ 50x=3\cdot75 \\ 50x=225 \\ x=\frac{225}{50} \\ x=\frac{9}{2} \end{gathered}$

If you read the question, so will see this part:

if you multiply both sides of the equation by 3 you get 50 x equals 75

This is the part where there is a problem. You did say to multiply by 3 (both sides). But don't multiply the right hand side of "75" mistakenly.

The last part of this line should be "equals 75 times 3"

This is the mistake.