P (three black balls) = 1-P (at least one red ball) = 1-0.5=0.5.

P (three red balls) = 1-P (at least one black ball) = 1-0.8=0.2.

All possibilities are as follows:

Three black balls, two black balls, one red ball, one black ball, two red balls, three red balls.

Namely: p (three black balls) +P (two black balls and one red ball) +P (one black ball and two red balls) +P (three red balls) = 1.

∴P (red and black balls)

=P (two black balls and one red ball) +P (one black ball and two red balls)

= 1-P (three black balls) -P (three red balls)

= 1-0.5-0.2

=0.3