A person crosses a 600 m long street in 5 minutes. What is his speed in km per hour?

### Concept & Multi-Step Conversion This problem requires calculating speed and then standardizing the units. First, calculate the speed in meters per second (m/sec), then convert that result into kilometers per hour (km/hr). $$ \text{Speed} = \frac{\text{Distance}}{\text{Time}} $$ $$ \text{Speed in km/hr} = \text{Speed in m/sec} \times \frac{18}{5} $$ ### Step-by-Step Solution * **Given:** Distance = $600$ m, Time = $5$ minutes. * **Convert Time to seconds:** * $5 \text{ minutes} = 5 \times 60 = 300 \text{ seconds}$. * **Calculate Speed in m/sec:** * $\text{Speed} = \frac{600 \text{ m}}{300 \text{ s}} = 2 \text{ m/sec}$. * **Convert Speed to km/hr:** * $\text{Speed in km/hr} = 2 \times \frac{18}{5}$ * $= \frac{36}{5}$ * $= 7.2 \text{ km/hr}$. ### Exam Strategy & Shortcut Alternatively, convert the original inputs directly to km and hours. Distance = $0.6$ km. Time = $5/60$ hours = $1/12$ hours. Speed = $0.6 / (1/12) = 0.6 \times 12 = 7.2$ km/hr. This avoids the $18/5$ multiplier entirely and is often faster if you are comfortable with fractions. ### Common Pitfall Using the $5$ minutes directly as seconds (calculating $600/5 = 120$ m/s) resulting in an absurdly high and incorrect final km/hr speed. Always ensure your time base is in seconds before using the $18/5$ conversion factor. ### Final Answer Therefore, the correct answer is **7.2**.