A rectangular field is 80 m by 70 m. A man walks round it at the rate of 3 km per hour. What time will he take in making 5 rounds ?

Answer

To solve the problem step by step, we will follow these calculations:

### Step 1: Find the Perimeter of the Rectangular Field
The formula for the perimeter (P) of a rectangle is given by:
\[ P = 2 \times ( \text{Length} + \text{Breadth} ) \]

Given:
- Length = 80 m
- Breadth = 70 m

Calculating the perimeter:
\[ P = 2 \times (80 + 70) \]
\[ P = 2 \times 150 \]
\[ P = 300 \text{ m} \]

### Step 2: Calculate the Distance for 5 Rounds
The distance for one round is equal to the perimeter. Therefore, for 5 rounds, the distance (D) will be:
\[ D = 5 \times P \]
\[ D = 5 \times 300 \]
\[ D = 1500 \text{ m} \]

### Step 3: Convert Distance from Meters to Kilometers
Since the speed is given in kilometers per hour, we need to convert the distance from meters to kilometers.
1 kilometer = 1000 meters, so:
\[ D = \frac{1500}{1000} \text{ km} \]
\[ D = 1.5 \text{ km} \]

### Step 4: Use the Speed to Calculate Time
The formula for time (T) when distance and speed are known is:
\[ T = \frac{D}{S} \]

Given:
- Speed (S) = 3 km/h

Calculating the time:
\[ T = \frac{1.5 \text{ km}}{3 \text{ km/h}} \]
\[ T = 0.5 \text{ hours} \]

### Step 5: Convert Time to Minutes
To convert hours into minutes, we multiply by 60 (since 1 hour = 60 minutes):
\[ T = 0.5 \times 60 \]
\[ T = 30 \text{ minutes} \]

### Final Answer
The man will take **30 minutes** to make 5 rounds around the rectangular field.

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