The physician ordered 50 mL of 1:20 W/V solution, diluted to 1000 mL. What is the ratio strength of W/V?

1:200
1:300
1:400
1:500

1:400

Rationale: The ratio strength of W/V is 1:400 . To calculate, begin with 1:20 = 5%. Therefore, 50 mL x 5% = 1000 mL x X%. This gives: 2.5 = 1000 x X%. Dividing by 1000 produces X = 0.25% or 1:400.