Difference over Sum Equation

[mathisp64]

1. The problem statement, all variables and given/known data
Real world use of (x-y)/(x+y).


2. Relevant equations
(x-y)/x


3. The attempt at a solution
(x-y)/x solves for the mean difference ratio. I had 400 oranges and sold 100. 400-100/400 gives .75 or 75% remaining. I do not understand where I would use the difference over sum equation. The answer: .6 or 60% using this equation baffles me.

Can anyone set me straight on this.

Thanks!!!

[tiny-tim]

hi mathisp64! welcome to pf! :smile:
(x-y)/x solves for the mean difference ratio. I had 400 oranges and sold 100. 400-100/400 gives .75 or 75% remaining. I do not understand where I would use the difference over sum equation. The answer: .6 or 60% using this equation baffles me.

you have a party with 70 girls and 62 boys …

(x-y)/(x+y) tells you how unbalanced it is :wink:

[mathisp64]

Thanks, that was exactly what I was needing to know.