s= {1,2,3 ................ 499,500}
n(A) = 500/3 = maximum 166 so probability divided by 3 is p(A) = 166/500
n(B) = 500/5 = maximum 100 so probability divided by 5 is p(A) = 10/500
n(A and B) = maximum 33 so probability divided by both 3 and 5 is p(A and B )= 33/500
p(A or B) = p(A)+P(B)-p(A and B)
p(A or B) = (166/500)+(100/500)-(33/500) = 233/500