Invitation to Computer Science 8th Edition

Sending a $100-$ character message, 800 bits, across a 100 million bit per second (100 Mpbs) Ethernet takes about $8 \times 10^{-6}$ seconds, or 8 $\mu s$. The the likelihood that one of the other 19 users on the system would transmit during that tiny window of time is quite small, so the probability of a the collision would be small.
Sending a $100-$ character message, 800 bits, across a 100 million bit per second (100 Mpbs) Ethernet takes about $8 \times 10^{-6}$ seconds, or 8 \musec. The the likelihood that one of the other 19 users on the system would transmit during that tiny window of time is quite small, so the probability of a the collision would be small.