comparing apples to apples

[S1ngram]

I'm pretty sure I read in one of these forums how to compare the cost of bleach when sold in different concentrations, but I just can't find it. If that didn't make sense, here's an example:

If 1 gallon of 6% costs $2 and 1 gallon of 12.5% costs $3.50, which is the better buy? Can I solve it like this? I think this may have been how the other poster figured it, but I just can't remember and my math skills are not the best.

100/6=16.67 x $2= $33.33
100/12.5= 8 x $3.50=$28.00

So if I was buying a 1 gallon bottle of 100% bleach (my clothes would never be the same) the 12.5% at $3.50 per gallon is the better deal. BTW...I have no idea what12.5% actually costs, so if my numbers are really low, I hope no one got excited that I had found it cheap somewhere :grin:

 

[DeeMac]

I downloaded this last year.....http://poncatechsquad.com/dan/chlorine/

 

[jmbradwell]

( Bottle Size ) X ( Concentration ) / 100 = ( total chlorine in bottle )
( Bottle Cost ) / ( Total Chlorine in Bottle ) = ( Cost per ounce )

128 oz Bottle of 12 % at $ 3.00

128 X 12 /100 = 15.36 ounces chlorine
$3.00 / 15.36 = $ 0.1953 cost per ounce

128 oz Bottle of 6% at $2.00

128 X 6 / 100 = 7.68 ounces chlorine
$2.00 / 7.68 = $0.2604 cost per ounce

The 12% is cheaper in the long run.

 

[S1ngram]

Thanks!

 

[JasonLion]

That works, though it depends on the container sizes being the same.

I divide the price by the product of the container size and the percentage to get $/pure oz. So:
$2/(0.06*128) = $0.26/oz
$3.50/(0.125*128) = $0.219/oz
In your example that comes out to the same thing, but it is easier to manage when the containers are different sizes.

 

[jmbradwell]

There is more than one way to skin a cat. Both methods work.

 

[zea3]

Check the dates on the 6% bleach, because it may be old and have lost some of its potency. Most grocery store bleach is now sold in smaller bottles with 8.25% concentration. Those started showing up on shelves last pool season.

 

[toofast]

Also keep in mind that 12% breaks down rather quickly...so sometimes even though 8.25% may be a few pennies more per ounce, in all reality the effective strength might wipe out that gain.