Answer :
If we have twice as many blue marbles as green, we have 3 parts; 2 parts blue and 1 part greens. Therefore, 1/3 of the marbles are green
54/3=18
At least 18 of the marbles are green
54/3=18
At least 18 of the marbles are green
[tex]b\ \ \ \rightarrow\ \ \ the\ number\ of\ blue\ marbles\\g\ \ \ \rightarrow\ \ \ the\ number\ of\ green\ marbles\\\\b+g \geq 54\ \ \ and\ \ \ b=2g\\\\2g+g \geq 54\ \ \ \Leftrightarrow\ \ \ 3g \geq 54\ \ \ \Leftrightarrow\ \ \ g \geq 18\\\\Ans.\ At\ least\ 18\ green\ marbles.[/tex]