# 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?

Sep 2, 2015

Average mass (per ball) $= 4.0$ g.

#### Explanation:

If $\frac{2}{3}$ of the balls are white

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 $2 \times 5.0 \text{ g" + 1xx2.0 " g "= 12.0 " g}$

and since there are $3$ balls in each group,
the average weight would be (12.0" g")/3 = 4.0 " g"