A tank holds 210 liters of a chemical solution Currently the

A tank holds 210 liters of a chemical solution. Currently, the solution has a strength of 10%. How much of this should and replaced with 80% solution to get a final strength of 30%?

Solution

x = amount needed of 80% solution

Amount of pure chemical remains after x is removed = 0.1*(210 - x)

Amount of pure chemical added back = 0.80*x

Amount of pure chemical in final mixture = 0.30*210

Initial amount of pure chemical = final amount of pure chemical

0.1*(210 - x) + 0.8*x = 0.3*210

0.7x = 63 - 21

0.7x = 42

x = 60 liters