GRE General TestQuantitative ReasoningHard
A satellite orbits Earth at a constant speed. If it completes 5 full orbits in 12.5 hours, what is its average speed in kilometers per minute, given that the length of one orbit is 40,000 kilometers?
- A2.67 km/min
- B0.5 km/min
- C3.33 km/min
- D26.67 km/min
Show answer & explanationAnswer & explanation
Correct answer: D. 26.67 km/min
Total distance = 5 orbits * 40,000 km/orbit = 200,000 km. Total time = 12.5 hours. Convert time to minutes: 12.5 hours * 60 minutes/hour = 750 minutes. Average speed = Total distance / Total time = 200,000 km / 750 minutes = 266.66... km/min. Rounding to two decimal places, 26.67 km/min.
Why the other options are wrong
- A. This is incorrect; it might result from dividing 200,000 by 12.5 (hours) instead of minutes (200000/12.5 = 16000), or other errors.
- B. This is incorrect; it might result from significant calculation errors or misinterpretation of units.
- C. This is incorrect; it might result from using 40,000/12.5 = 3200, or other errors.
Unit Rate and Conversion
Unit rate is a rate expressed as a quantity of one unit. Solving problems often requires converting units (e.g., hours to minutes, miles to kilometers) to ensure consistency in the rate calculation.
- Speed = Distance / Time.
- Conversion factors are essential (e.g., 1 hour = 60 minutes).
- Ensure all units are consistent before calculating the rate.
Memory trick: Distance over time, with consistent units.