Calculate the masses of potassium hydroxide and water, which are necessary to prepare

Calculate the masses of potassium hydroxide and water, which are necessary to prepare a solution of 80 g with a mass fraction of alkali of 20%.

Given:
m solution = 80 g
W = 20%
To find:
m (KOH) =?
m (H2O) =?
Solution:
1) Let’s write the formula for solving the problem
W = (m substance: m solution) x 100%
m substance = (W x m solution): 100%
2) Find the mass of potassium hydroxide
m (KOH) = (20% x 80 g): 100% = 16 g.
3) Find the mass of water
m solution = m substance + H2O
m (H2O) = m solution – m substance
m (H2O) = 80 g – 16 g = 64 g.
Answer: m (KOH) = 16 g; m (H2O) = 64 g.