Introduction / Context:
This is a straightforward time and distance question that checks whether you can correctly convert units between metres per minute and kilometres per hour. Such conversions are very common in aptitude tests and form the foundation for more advanced time and distance problems.
Given Data / Assumptions:
- Length of the street = 600 metres.
- Time taken to cross the street = 5 minutes.
- We must find the walking speed in km/h.
- The person walks at a constant speed.
Concept / Approach:
Speed is defined as distance divided by time. However, because the required unit is km/h, we need to convert 600 metres to kilometres and 5 minutes to hours. Basic conversions are:
- 1000 metres = 1 kilometre.
- 60 minutes = 1 hour.
After converting, we compute speed = distance / time in the desired units.
Step-by-Step Solution:
Step 1: Distance = 600 metres = 600 / 1000 km = 0.6 km.
Step 2: Time = 5 minutes = 5 / 60 hours = 1 / 12 hour.
Step 3: Speed = distance / time = 0.6 / (1 / 12).
Step 4: 0.6 / (1 / 12) = 0.6 * 12 = 7.2.
Step 5: Therefore the walking speed is 7.2 km/h.
Verification / Alternative check:
Alternatively, calculate speed in metres per minute first. Distance is 600 metres in 5 minutes, so speed = 600 / 5 = 120 metres per minute. Now convert to km/h: 120 metres per minute * 60 minutes per hour = 7200 metres per hour, or 7.2 km/h. This matches the previous method and verifies the answer.
Why Other Options Are Wrong:
- 3.6 km/h: This is half of 7.2 and may arise from forgetting a factor of 2 during conversion.
- 8.4 km/h: Slightly higher than the true value and likely results from an error in division.
- 10 km/h: Too high and does not correspond to the given distance and time.
Common Pitfalls:
- Confusing metres with kilometres and minutes with hours.
- Using 5/100 instead of 5/60 when converting minutes to hours.
- Inverting the speed formula and accidentally computing time / distance.
Final Answer:
The walking speed of the person is
7.2 km/h.
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