If a solution contains 9 mg of salt per 1000 mL, how many mg of salt are needed for 250 mL?

If a solution contains 9 mg of salt per 1000 mL, how many mg of salt are needed for 250 mL?

• A. 1.25
• B. 2.25
• C. 2.0
• D. 3.0

Answer: (B)

This question tests proportionality and how to scale a given quantity to a different volume. If you have 9 mg of salt in 1000 mL, the amount per mL is 9/1000 = 0.009 mg/mL. For 250 mL, multiply: 0.009 × 250 = 2.25 mg. Another quick way is to note that 250 mL is a quarter of 1000 mL, so the amount is a quarter of 9 mg, which is 9 ÷ 4 = 2.25 mg. So 2.25 mg of salt are needed.

This question tests proportionality and how to scale a given quantity to a different volume. If you have 9 mg of salt in 1000 mL, the amount per mL is 9/1000 = 0.009 mg/mL. For 250 mL, multiply: 0.009 × 250 = 2.25 mg. Another quick way is to note that 250 mL is a quarter of 1000 mL, so the amount is a quarter of 9 mg, which is 9 ÷ 4 = 2.25 mg. So 2.25 mg of salt are needed.