A person standing between two vertical cliffs and 640 m away from the nearest cliff, produces sound. He hears the first echo after 4 s and the second echo 3 s later. Calculate :
the distance between the cliffs

Explanation

To solve the problem of calculating the distance between the two cliffs based on the echoes heard by the person, we can follow these steps:

### Step 1: Understand the Scenario
The person is standing 640 meters away from the nearest cliff. When he produces a sound, it travels to the nearest cliff and back, which creates the first echo. He hears this echo after 4 seconds.

### Step 2: Calculate the Speed of Sound
The distance traveled by sound to the nearest cliff and back is:
\[ \text{Distance} = 2 \times 640 \text{ m} = 1280 \text{ m} \]
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