Respuesta :
An observer in one of those galaxies see the other galaxy moving away at 400000 km/s.
Relative velocity is the velocity of an object with respect to another object, that is the time rate of change of relative position of one object with respect to another object.
Since two galaxy are moving in opposite directions with a velocity of 200,000 km/s. Hence the relative velocity between the two galaxies is 400000 km/s (200000 + 200000)
Therefore an observer in one of those galaxies see the other galaxy moving away at 400000 km/s.
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