How many liters of water should be added to 20 liters of 40% solution of acid to obtain 30% solution?

Answer 1

Acid = 0.4 * 20 = 8 liters.
Water = 0.6 * 20 = 12 lites.

A / (A + W) = 0.30,
8 / (8 + W) = 0.30,
2.4 + 0.3W = 8,
0.3W = 8 - 2.4 = 5.6,
W = 18.7 Liters.

18.7 - 12 = 6.7 Liters of water added.

Answer 2

x = liters of water

.40(20) = .30(x + 20)

8 = .30x + 6

8 - 6 = .30x + 6 - 6

2 = .30x

2 / .30 = .30x / .30

6.666 = x (which is also 6 2/3 as a fraction)

6.7 ~ x

6.7 liters of water is needed.

or

Six and two-third liters of water is need to obtain a 30% acid solution.