Read the speedometer and report the speed to the proper number of digits in miles per hour (mph) and kilometers per hour (km/h). speed: mph speed: km/h
The Correct Answer and Explanation is:
Speed: 120 mph Speed: 200 km/h
The speedometer needle is pointing precisely at 120 on the outer scale, which is marked in miles per hour, and at 200 on the inner scale, which represents kilometers per hour. This suggests that the vehicle is traveling at a speed of 120 mph or 200 km/h. These values are reported with three significant digits, which is appropriate given that the speedometer markings are clearly labeled at intervals of 20 units.
Speedometers are analog instruments that measure a vehicle’s speed based on the rotation rate of the wheels or transmission. In this case, the speedometer displays two concentric scales: one for mph, commonly used in the United States, and one for km/h, used in most other countries around the world. This dual-scale design enables drivers to easily adjust to regional speed regulations, especially when driving internationally.
The accuracy of a speed reading depends on the clarity of the tick marks and how precisely the needle aligns with those marks. When a needle is exactly aligned with a labeled tick, the correct approach is to report the value to the same number of significant digits as displayed. For instance, 120 mph and 200 km/h are both provided with three digits, suggesting a precision of ±1 unit based on standard analog gauge interpretation.
Reporting speed with the correct number of digits is important because it reflects both the precision of the measurement and the limitations of the instrument. Overstating accuracy by including extra digits (such as 120.0 mph) would imply a precision the instrument does not support. Conversely, understating the measurement by writing just “120” without the unit or precision context could cause misinterpretation. In scientific and engineering contexts, clarity and appropriate precision ensure that data can be reliably used and compared.
