If white balls have a mass of 5.0 grams and black balls have a mass of 2.0 grams, in a box containing white and black balls with #2/3# of the balls being white, what is the average mass of a single ball in this box?
Average mass (per ball)
then we could group the balls into groups of 3 with 2 white balls and 1 black ball in each group.
Each group would weight
and since there are
the average weight would be