# Thread: trying to work out what probably is a pretty basic formula.

1. ## trying to work out what probably is a pretty basic formula. (solved)

i'm trying to work out what steps i need to take to calculate the number that makes the following true...

(719 + 728 + 692 + 719 + X) / 5 = (719 + 728 + X) / 3

i know the answer is about 670 but don't know how to work it out.

can anyone help?

2. First it would help if you'd learn some LaTeX, so people can actually read what you've posted...

I assume it's

$\frac{719+728+692+719+x}{5} = \frac{719+728+x}{3}$

$\frac{2858+x}{5} = \frac{1447 + x}{3}$

$3(2858 + x) = 5(1447 + x)$

$8574 + 3x = 7235 + 5x$

$1339 = 2x$

$x = 669.5$.

3. ok, sorry about that. but that's excellent, i can see what i needed to do. i appreciate that a lot.