10. There are three piles of chess pieces, each pile has the same number of pieces, and they are only black and white. The number of black pieces in the first pile is the same as the number of white pieces in the second pile. The black pieces in the third pile account for two-fifths of all the black pieces. If these three piles of chess pieces are combined, what fraction of the total pieces are white?
10.【Solution】Assume the second pile is entirely black stones, and the first pile is entirely white stones, (i.e., swap the black stones in the first pile with the white stones in the second pile)

The black stones in the second pile are $\frac{1}{3}$ of all the stones, and at the same time, they are $1-\frac{2}{5}$ of the black stones, so the black stones account for: $\frac{1}{3} \div\left(1-\frac{2}{5}\right)=\frac{5}{9}$ of all the stones.
The white stones account for: $1-\frac{5}{9}=\frac{4}{9}$ of all the stones.