Some of these and some of those (Posted on 2018-04-30)
One day on the board, Ms. Math wrote the digits 1 to 9. She then wrote a
certain number of fives and also a number of eights. The number of fives and the
number of eights were not necessarily the same. The mean (average) of all the
digits on the board is 6.4.
Determine the smallest number of digits that can be on the board