Question

12) A bag contains 3 red marbles, 4 black

Answer 1

3+ 4 + 5 = 12

So the chance of picking a marble that is not black is minus it

3+5 = 8 marbles are not black

Take 8 divided to the whole number which is 12

8/12= 66%


Hope this helps!

Answer 2

$|\Omega|=3+4+5=12\\|A|=3+5=8\\\\P(A)=\dfrac{8}{12}=\dfrac{2}{3}\approx66.7\%$