One/Two Variable Equations

Question

If 5x=3y, what is x+y?

Fairly basic math problem but whenever I solve for one of the variable when I plug it back into the problem I end up with no solution. I have 5 other problems similar to this.

Answer 1

You can solve this equation for x or y and get an expression that would allow you to determine either variable given the value of the other.

For example, If you solve for y:

Divide both sides of the equation by 3: 5/3 x = 3/3 y

so 5/3 x = y

Then you can substitute a given value for x and determine y.

If you solve for x:

Divide both sides by 5: 5/5 x = 3/5 y

so x = 3/5 y

Then you can substitute a given value for y to determine x

Answer 2

You don't have this in the form of 2 equations and 2 unknowns, so you cannot solve for x and y. (you have just one equation, and an expression.

As presented, the only thing you could do is to solve the equation for x or y, and then substitute it into the expression.

Example:

5x = 3 y

therefore: x = 3y/5

So: the value of x + y is y + 3y/5 = 0.6y