Answer:
28 non-blue marbles.
Step-by-step explanation:
Initial probability of choosing a blue marble = 4/12
Let the number of non-blue marbles to be added be x.
[tex]\frac{4}{12+x} =\frac{1}{10}[/tex]
[tex]12+x=40[/tex] (cross multiply)
[tex]x=28[/tex]
