Final answer:
When no speed limit is posted for a school crossing, the limit can vary by location. Typically, a low speed limit is expected to ensure pedestrian safety. Local traffic laws should be consulted for the exact speed limit.
Step-by-step explanation:
The posted speed limit when no limit is provided for approaching a school crossing can vary by jurisdiction, and it is essential to be aware of local traffic laws. However, the general guideline in many areas, when not otherwise posted, would be to follow a low speed limit that ensures the safety of pedestrians. Since none of the provided options match the reference information of typical residential speed limits, this question might be region-specific, or it could be seeking an approximate answer based on common practices. The student should verify with local traffic regulations for the most accurate answer.
It's important to note that when approaching a school crossing, drivers should always prioritize safety over speed. It is also beneficial to understand that speeds mentioned in various units such as kilometers per hour and meters per second can be converted to understand speed limits better. For instance, 50 kilometers per hour is equal to approximately 31 miles per hour, and 100 km/h is the same as 62 miles per hour or about 27.8 meters per second.