Answer :
Well 60% of the school is girls so 40% must be boys.
50% of girls walk so 50% of 60% or 30%(0.6*0.5) of the school must walk
20% of boys walk so 20% of 40% or 8%(0.4*0.2) also walk
Thus 30%+8%=38%
50% of girls walk so 50% of 60% or 30%(0.6*0.5) of the school must walk
20% of boys walk so 20% of 40% or 8%(0.4*0.2) also walk
Thus 30%+8%=38%