To find average of any number of quatities of the same kind is, to add all the items together and then divide the sum by the number of items.

Average = Sum of all the given quantities
Number of the given quantities

If a man earns Rs. 20, Rs. 25, Rs. 28, Rs. 23 and Rs. 24 on five consecutive days of week, he earns a total of

= Rs. (20+25+28+23+24) = Rs. 120

To find his average earning per day, his total earning is divided by the number of days.

Average earning per day = 120/5 = Rs. 24

Average earning does not mean that the man earned everyday Rs. 24. But had he earned Rs. 24 everyday , his total earning in 5 days would have been 5 x Rs. 24 = Rs. 120