60 percent of the energy is lost. Then use energy conservation as follows:
Here, m is the mass of the ball, h is the height from where the ball is dropped, h1 is the required height and g is the gravitational acceleration.
On further solving the above equation, we get,
mgh=mgh1 + (60100)mgh
h = h1 + 0.6hh1 = h(1−0.6)
h1 = 0.4h
On simplifying the above relation as,
h1 = 0.4hh1 = 2/5h
Therefore, the ball will rebound upto the height of 2/5 times the given height.