Red marbles are \(\frac{2}{5}\) of total

Green marbles are \(\frac{1}{4}\) of total and

Blue marbles are \(\frac{1}{5}\) of total.

qty A = \(\frac{2}{5}\) of x where x is the no of marbles.

qty B = (\(\frac{1}{4} + \frac{1}{5}\)) of x where x is the no of marbles.

hence qty B = \(\frac{9}{20}\) of x

\(\frac{2}{5}\)< \(\frac{9}{20}\) hence whenever x is +ve number qty B will always be greater than A and in this case no of marbles must be atleast 1 so B is greater.

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes

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