Out of 60 days a person arrives before 8.30 am for = 39 days
So remaining days left are = [tex]60-39=21[/tex] days
So probability that a person will arrive after 8.30 am is = [tex]\frac{21}{60}[/tex]
or [tex]\frac{7}{20}[/tex]
Hence, probability is [tex]\frac{7}{20}[/tex]