1. Every day at 5 PM when school is over, Xiao Ming's father always drives from home to pick him up on time and take him back. One day, the school dismissed an hour early, and Xiao Ming walked home by himself. On the way, he met his father who was coming to pick him up, and as a result, they arrived home 20 minutes earlier than usual. Then Xiao Ming walked for $\qquad$ minutes before meeting his father.
二、1.50 minutes.
As shown in Figure 6, Xiao Ming
starts walking home from point $A$
and meets the car coming to pick him up
at point $C$. As a result, the car returns from $C$ to $B$ 20 minutes earlier than usual. This indicates that the car takes 20 minutes to travel from $C$ to $A$ and back to $C$.
Therefore, the car takes 10 minutes to travel from $C$ to $A$.
Thus, the car meets Xiao Ming at $4:50$, meaning Xiao Ming has been walking for 50 minutes when he meets his father.