Question

A circular tank of diameter 2 metre is dug and the earth removed is spread uniformly all around the tank to form an embankment 2 metre in width and 1.6 metre in height. Find the depth of the tank

Answer 1

volume of embankment= volume of cylindrical tank
note R=3 and r=1


so,
π [R'2 -r'2]×h=. πr'2h

thus by putting given values
we get
h=4.8m

Answer 2

for circular tank

external radius    R = 3 m
internal radius      r = 1 m

thus  volume of embankment

V = pi (R^2 - r^2) * h
    = pi (9-1) * 1.6
     = 40.192 m^2

now volume of tank

V' = pi r^2 h
     = 3.14 * 1 * h

since both are equal

V = V'
thus
                        3.14 h  = 40.192
                                h = 12.8 m

thus height of tank is 12.8 m