The mass of a sample is 550 milligrams. Which of the following expresses that mass in kilograms?

• A. 0.00055 kg
• B. 0.0055 kg
• C. 0.55 kg
• D. 0.055 kg

Answer: (A)

Verified step by step guidance

1. Identify the given mass and its unit: 550 milligrams (mg).
2. Recall the conversion factors between units of mass: 1 kilogram (kg) = 1000 grams (g), and 1 gram = 1000 milligrams (mg).
3. Convert milligrams to grams by dividing the mass in milligrams by 1000: \(\text{mass in grams} = \frac{550}{1000}\) mg.
4. Convert grams to kilograms by dividing the mass in grams by 1000: \(\text{mass in kilograms} = \frac{\text{mass in grams}}{1000}\).
5. Combine the two steps into one conversion from milligrams to kilograms: \(\text{mass in kilograms} = \frac{550}{1000 \times 1000} = \frac{550}{1,000,000}\).