Data:
Total Events/Sample Space/No. of People = 1000
People having Blood Group A = 300
People having Blood Group B = 325
People having Blood Group O = 250
People having Blood Group AB = 125

Solution:
Probability of having Blood Group AB = People having Blood Group AB / Total Number of People

Probability of having Blood Group AB = 125/1000
Probability of having Blood Group AB = 0.125