Probability of Salary Day being a Monday = 1/7 Probability of Salary Day being a Tuesday = 1/7 Probability of Salary Day being a Wednesday = 1/7 Probability of Salary Day being a Thursday = 1/7 Probability of Salary Day being a Friday = prob(Fri) + Prob (sat) + Prob(Sun) = 1/7 + 1/7 + 1/7 = 3/7

Hence you feel that the salary mostly arrives on a Friday