Help me with a chemistry problem(?)

[LotC]

It's been about a million years since I've solved one of these so the method by which to do so has slipped into the mists of time.

Anyway, say you have a solution of 30%x and 70%y, totaling 30L. You want to make it a 50% solution. How many liters would you have to drain off and top up with x in order to get it to 50%?

I know I'll smack myself in the head once someone posts the solution.

Edit: You want to end up with 30L of 50% solution.

[LordShiva]

You have 9l of x, 21l of y, and you want 15l of x/15l of y. Every litre you drain loses you 0.3l of x and 0.7l of y. If you drain 8.57 (6/0.7) litres of solution, you end up with 15l of y. Now fill teh solution with 8.57l of x.

[Krill]

That's chemistry?

[Combat Ingrid]

You start with a solution containing 9 liters x and want the final solution to contain 15 liters x.

For each liter you replace, you remove 0.3 liters x and add 1 liter x.

The amount you need to replace is z liters, which means: 9 - 0.3z + z = 15 -> z = 8.57

Edit: LS gets the cookie

[LotC]

Originally posted by Krill
That's chemistry?

No, I suppose it's not.

Thanks guys.

[SlowwHand]

Originally posted by Combat Ingrid


Edit: LS gets the cookie

You both get my sympathy. They both make me hurt just to read them.

[Lazerus]

It's more basic maths then chemistry.

[BeBMan]

Teh SuperShiva

I'm just wondering if LotC is a relative of LOTM

[SpencerH]

If you actually worked in a lab you'd just make the 50% solution. Did some science teacher call that chemistry? Bah!