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A transmitting antenna is kept on the surface of the earth. The minimum height of receiving antenna required to receive the signal in line of sight at 4 km distance from it is x × 10 –2 m. The value of x is __. (Let, radius of earth R = 6400 km)

1. 125
2. 1250
3. 12.5
4. 1.25

Correct answer: 125

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