A rod of mass 'M' and length '2L' is suspended at its middle by a wire. It exhibits torsional oscillations; If two masses each of 'm' are attached at distance 'L/2' from its centre on
both sides, it reduces the oscillation frequency by 20%. The value of ratio m/M is close to :
a. 0.77
b. 0.57
c. 0.37
d. 0.17