In a particular year there were exactly four Mondays in January as well as exactly four Fridays that month. What day of the week was January 1?
A 31 day month has 3 days that occur exactly five times. They must be consecutive - thus Tuesday, Wednesday, Thursday.
So Tuesday was the 1st, Thursday is the 31st.
Checking my calendar, the next instance of this will be the year 2019.
Posted by Jer
on 2017-01-09 13:41:41