Solution: let the wrong questions of the small square account for x of the total number of questions.

Xiaoming's wrong answers account for the total number of questions: 1/3*2= 1/6.

1/6+x= 1/5

x= 1/30

1/30=7, and the total number of topics is 30*7=2 10.

2 10/2= 105 (road)

105* 1/3=35 (Road)

105-35=70 (highway) 105-7=98 (highway)

70+98= 168 (highway)