x1=1/4,x1+x2=2→1/4+x2=2,→x2=7/4,→
a1=1/4,a2=3/4,a3=5/4,a4=7/4,
m=(1/4)×(7/4)=7/16
n=(3/4)×(5/4)=15/16
∴|m-n|=8/16=1/2