Yellow balls account for 56+4 80 = 3 4 = 75% of the total.

A: The percentages of yellow balls and blue balls in the box are 75% and 25% respectively.

(2) The ratio of labeled ball is1012 = 56;

The number of yellow balls is:

80÷ 5 6 × 3 4 ,

=80× 6 5 × 3 4 ,

=72 (pieces);

There are 72 yellow balls in the box.