Percentage of particles bounce off a rigid body

I have particle system which emits 2000 particles. These particles hit a rigid body , but not all particles hit rigid body. Some particles, which collide with rigid body bounce off and other just flow straight. Out of 2000 particles lets say 800 particles hit rigid body and bounce off and rest of particles ( 1200 particles) just flow though. So 40% of total particles bounce off. How can I calculate this percentage from the script. Any help or suggestions are welcome.