Solution: Let the width of hardened pavement around P and Q green spaces be x meters. According to the meaning of the question, it can be concluded that

(60-3x)×(40-2x)=60×40× 1/4

X= 10 or x=30.

After inspection, x2=30 does not meet the meaning of the question, so it is discarded.

Answer: The width of hardened pavement around the two green areas is10m.