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

• Aug 15th 2010, 01:46 AM
val1
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?
• Aug 15th 2010, 01:50 AM
Prove It
First it would help if you'd learn some LaTeX, so people can actually read what you've posted...

I assume it's

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

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

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

$8574 + 3x = 7235 + 5x$

$1339 = 2x$

$x = 669.5$.
• Aug 15th 2010, 02:12 AM
val1
ok, sorry about that. but that's excellent, i can see what i needed to do. i appreciate that a lot.