If a pharmacist mixed 1 pint of propylene glycol having a specific gravity of 1.20 with 500 mL of water, how many milliliters additional propylene glycol should be added to change the specific gravity to 1.15?

Question

Please help with how to do this problem. I've tried many alligation steps and can't seem to get the answer.

Answer 1

you want this basic algebra equation (first change pint to 483ml)

483ml*1.20+V*1.20+500*1=(V+483+500)1.15

solve for V of additional ml of glycol.

V(1.20-1 )=1.15(983)-1.2(483)-500
V=I get 254ml

check that.

Answer 2

Thank you for your help. The answer in the textbook is 1031.38 mL propylene glycol. There is no detailed explanation in the textbook on how to get to the answer. Also, 1 pint = 473 mL.