Answer:
Mix (1/3) part water with 1 part fruit juice.
Explanation:
One approach follows:
1 part water ↔ 3 parts fruit juice
Divide both sides by 3:
(1/3) part water ↔ 3/3 parts fruit juice (same as 1 part fruit juice)
Answer: Mix (1/3) part water with 1 part fruit juice.