First developed in the early 1960s by behavioural psychologist John S. Adams, equity theory is concerned with defining and measuring the relational satisfaction of employees.
For 31 days in a month: (31 days/month) / (7 days/week) = 4.4286 weeks/month. For 30 days in a month: (30 days/month) / (7 days/week) = 4.2857 weeks/month. For 28 days in a month: (28 days/month) / (7 days/week) = 4 weeks/month. For 29 days in a month: (29 days/month) / (7 days/week) = 4.1429 weeks/month.
Every year has 7 months with 31 days. Each of these months have at least 3 weekdays that happen 5 times during the month. For example, August 2014 has 5 Fridays, 5 Saturdays and 5 Sundays. October 2014 has 5 Wednesdays, 5 Thursdays and 5 Fridays.