golekeeper
Explanation:
because they use hand to save keeper
Explanation:
Below is an attachment containing the solution.
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The refractive index of water is

. This means that the speed of the light in the water is:

The relationship between frequency f and wavelength

of a wave is given by:

where v is the speed of the wave in the medium. The frequency of the light does not change when it moves from one medium to the other one, so we can compute the ratio between the wavelength of the light in water

to that in air

as

where v is the speed of light in water and c is the speed of light in air. Re-arranging this formula and by using

, we find

which is the wavelength of light in water.
Answer:
using a formula
average velocity=total displacement/total time
average velocity=120/1minute40sec
1minute=60sec
60sec+40sec=120sec
average velocity=120m/120sec
average velocity=1m/sec