Equity theory, most popularly known as equity theory of motivation, was first developed by John Stacey Adams, a workplace and behavioral psychologist, in 1963.
On average there are about 4.3 weeks in a month. Each week is 7 days, and there are normally either 30 or 31 days in a month, so there are usually between 4.2 and 4.4 weeks per month. The exception is February because it has fewer days, so there are about 4 weeks in that month. On average there are about 4.3 weeks in a month.
If you use that average to say how many weekdays there are in February you'd be off by almost two days since there will always 20 weekdays in Feb. In month with 31 days depending on the day of the week the month starts you could have as little as 21 days and as many as 23.