Answer:
Reach him in less than 5.0 seconds.
Step-by-step explanation:
Waves travel through different materials at different speeds.
Generally, more solid or rigid materials will transmit vibrational waves faster than softer or more fluid materials.
Even though the waves traveling through the gym's floor are probably too small to see, they will travel much faster than similar waves in a pool of water.
This is why Ian will feel the bouncing ball on the floor in less than 5.0 seconds.