Completed the whole journey:1-3/10 = 7/10.

At the same time, Xiao Ming walked the whole journey:

7/ 10- 1/2= 1/5

Dad's speed is Xiao Ming's:

7/ 10/ 1/5 = 7/2 times

The same distance takes Xiao Ming 2/7 of the time.

The remaining 3/ 10 distance, Xiao Ming needs to walk:

5 minutes (1-2/7)=7 minutes.

Xiao Ming needs to walk from home to school:

7÷3/ 10=70/3 minutes =23 minutes and 20 seconds