A lab technician needs to make a 90 liter batch of a 20 % acid solution . How can the lab technician combine a batch of acid solution that is pure acid with another that is 10% to get the desired concentration

Thank you for the opportunity to help you with your question!

Let x = amt of pure acid
the result is to be 90 liters, therefore
(90-x) = amt of 10% solution required:
.10(90-x) + x = .20(90)
9 - .1x + x = 18
.9x = 18 - 9

.9x = 9
x = 9/.9
x = 10 liters of pure acid required
then
90 - 10 = 80 liters of the 10% solution required:
See if that checks out
.10(80) + 10 = .20(90)
8 + 10 = 18; confirms our answer

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