I have a prescription for aminosyn 2.5% 500ml. On the pharmacy shelf, I only have a 8.5% 500ml. How do I prepare this order?

I know the answer is to add 235 ml of 8.5% aminosyn with steril water to 500 ml. I need to know the steps to getting that answer. It's obviously some sort of dilution. I need that 8.5 to get down to 2.5 in 500ml...but how, what are the steps/formula?

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Let's say you don't know how much aminosyn to add to how much water, which I assume is the problem. Let the amount of aminosyn be x, and the amount of water be y.

Then, x + y = 500.

Also, you know how much pure aminosyn you need, so

8.5% of x + 0% of y = 2.5% of 500

.085x +0y = .025(500)

Now you have a system of equations:

x + y = 500

.085x + 0y = .025(500)

Solve them and you will get the answer you want.

Let amount of aminosyn be x ml and amt of water be y ml

x+y=500

8.5% ofx + 0% of y= 2.5% of 500

0.085x= 1250

x (water)= 147 ml (to 3sf), so it means using 147 ml of this solution and dilute it into 500ml of solution. The amount of water would be:

amt. of water= 500-147= 353ml

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