Our family shares all the minutes in your cell phone plan. every 30 days you get 4,800 minutes. four people share the minutes. how many minutes can each person use per day if the minutes are split fairly?

"Fairly" is a loaded word. Perhaps you want to split the minutes so that each of 4 people gets the same number.
.. (4800 min)/(30 day)*/(4 person)
.. = 4800/(30*4) min/day
.. = 40 min/day/person

Each person can use 40 minutes per day.

That depends on the size of the month
Sept Apr June Nov all have 30 days.
4800/4 = 1200 (monthly allotment per month) / person
1200 / 30 = 40 minutes per day.

All the others have 31 days
4800 / 4 = 1200 minutes per month
1200/31 = 38.71 minutes per day = 38 minutes 42 seconds Don't make that last 42 seconds to your boy friend/girl friend.

Except February which has 29 days on leap years.
Each has 1200 minutes per month
1200/29 = 41.37 minutes = 41 minutes 22 seconds.
or
February has 28 day days most years.
each person has 1200 minutes per month.
1200 / 28 = 42.86 minutes = 42 minutes and 51 minutes 

The mode of the numbers is 29.