To minimize neutron leakage from a reactor, the ratio of the surface area to the volume should be a minimum. For a given volume V the ratio of the sphere will be
.
We know that the surface area and volume of the sphere is given by:

Therefore, the ratio between the surface area and the volume for the sphere will be:

Equating the volume to the constant c, we will find the value of
.

Substituting the value of r in the ration between surface area and volume, we get:

Calculating the constants, we get:

Hence, the ration between surface area and volume is 
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Your answer is.......a car moved 60 km East and 90 km in west.
Magnitude of acceleration = (change in speed) / (time for the change).
Change in speed = (27 - 0) = 27 m/s
Time for the change = 10 s
Magnitude of acceleration = (27 m/s) / (10 s) = 2.7 m/s² .