Completely inelastic collisions:
A perfectly inelastic collision is a collision in which the objects stick together after the collision and move with the same velocity.
The momentum of the system is conserved but the kinetic energy of the system is not conserved in an inelastic collision. This means that there will be some loss of kinetic energy.
How much KE will be lost?
This depends on the system that we are analyzing. There is no hard and fast rule that this amount of KE will be lost.
We cannot say that there will be exactly a 10% loss in KE without knowing the system.
Therefore, the given statement seems to be false.