Question

A pot contains 6 liters of brine at a concentration of 120g/l. How many liters of the water should be boiled off so that concentration of the brine is 200g/l.

Answer 1

divide 200 by 120 to get your answer

Answer 2

let the amount boiled off be x L

amount of brine = 6 (120 g/L) = 720 g
that must stay constant

(6-x)(200 g/L) = 720 g
1200 - 200x = 720
-200x = -480
x = 2.4

2.4 L must be boiled off


check:
liquid left = 6-2.4 = 3.6 L
but there must still be 720 g in there
concentration = 720/3.6 = 200 g/L