Answer :
SOLUTION
Notice that the total number of marbles are
[tex]12+24+14=50[/tex]The probability of not grey means it could be white or black
Hence
P(not grey) = P(white or black)
Since there are 12 whites and 14 blacks the the P(white or black) is
[tex]\begin{gathered} P(WorB)=\frac{12}{50}+\frac{14}{50} \\ P(WorB)=\frac{26}{50} \\ P(WorB)=\frac{13}{25} \end{gathered}[/tex]Therefore the P(not gray) is:
[tex]P(not\text{ gray\rparen=}\frac{13}{25}[/tex]