In a function, girls were allowed to wear only red, blue, or black dresses. If 15 girls were wearing red, 10 girls were wearing blue, and 20 girls wer...

In a function, girls were allowed to wear only red, blue, or black dresses. If 15 girls were wearing red, 10 girls were wearing blue, and 20 girls were wearing black, then the probability that a girl selected at random was not wearing a black dress is: