How many liters of water should be added to a 25% anti-freeze to obtain 30 L of a 20% solution ?

Question

Math  and algebra one 

Answer 1

If the solution is 25% antifreeze, it is 75% water.

Since we are adding pure water with no antifreeze we will work

the problem using water concentrations instead of antifreeze concentrations.

 

If we have x liters of 75% water that is 0.75x Liters of water.

To this we add 30-x liters of water

We end up with a total of 80% water in 30 L or 0.8(30) liters water

 

0.75x + (30-x) = 0.8(30)

-0.25x + 30 = 24

-0.25x = -6

x = 24 L

 

We started with 24 liters of the 25% antifreeze.

To this we add 6 liters of water to get 30L of 20% antifreeze solution.