Swim 2km at 3km/h. Run at 12km/h for 1 ½ hours. Cycling 55km at 30 km/h. What is the mean overall speed.

t1 = S1 / V1 = 2 km / 3 km/hr = 2/3 hr        where S1 = 2 km

S2 = 12 km/hr * 3/2  hr = 18 km      where t2 = 3/2 hr

t3 = S3 / V3 = 55 km / 30 km/hr = 11/6 hr   where S3 = 55 km

T = t1 + t2 + t3 = 4/6 + 9/6 + 11 / 6 = 24/6 = 4 hrs

S = S1 + S2 + S3 = 2 + 18 + 55 = 75 km

V =  S / T = 75 km / 4 hrs = 18.75 km/hr     for the average speed

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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