2 brown, 8 yellow, 8 green, thus our sample space is 2+8+8 = 18.
What is the probability that the card is NOT yellow? How many non-yellow are there? well 2 + 8 = 10, favorable outcomes.
[tex]\bf \cfrac{\stackrel{\textit{favorable outcomes}}{10}}{\underset{\textit{sample space}}{18}}\implies \cfrac{5}{9}\implies 0.\overline{555}\qquad \approx \qquad 55.6\%[/tex]