# Math Help - Trying to figure out cost

1. ## Trying to figure out cost

Alright, I am new here, I am going to try and explain this as well as I can.

I have a product that I paid 22.50 for. It was 280 watts with 1 rail at an efficiency level of 85. Now I have deduced the cost per watt, that was easy. However I am trying to find a constant (I guess). If I am paying .08036 per watt, how can I find if I am paying to much for a product. There are multiple levels of efficiency (85, 88, 90, etc) and you can have any number of rails (1,2,3, etc) that would come apart of the equation.

So, is there a constant that I can say, with x rail and at efficiency level x and x watts, this is what the price should be at.

I hope I explained this well. If you have any questions please ask. Thanks for your time.

2. ## Re: Trying to figure out cost

Hey onlyname.

For the efficiency, does this mean that 100% effeciency uses only the needed power, but 50% efficiency requires twice as much power to actually do what's meant to do?

If this is the case, then it would make sense to take into account efficiency is to take the per watt rating and divide by the efficiency where this is a number from 0 to 1 inclusive. If 100%, then nothing changes: if its 50% you double the figure, 25% you quadruple and 0% then you can't supply enough to get the job done.

To convert a percentage to a fraction simply divide by 100.

3. ## Re: Trying to figure out cost

Can you explain this for me in more detail.

"If this is the case, then it would make sense to take into account efficiency is to take the per watt rating and divide by the efficiency where this is a number from 0 to 1 inclusive. If 100%, then nothing changes: if its 50% you double the figure, 25% you quadruple and 0% then you can't supply enough to get the job done."

I am lost on the number 0 to 1 inclusive.

4. ## Re: Trying to figure out cost

The 0 corresponds to 0% and the 1 corresponds to 100%, that's all.

5. ## Re: Trying to figure out cost

Okay, so 50% would be .5, 80% .8, correct?

6. ## Re: Trying to figure out cost

Yes that's correct, and remember to divide your per watt figure by your efficiency (i.e. pw = per watt, e = effeciency then pw/e).