A bag contains green, blue and yellow glass marbles.
The ratio of green to blue glass marbles is 2 : 7.
The ratio of green to yellow glass marbles is 3 : 5.

Let g = number of green marbles, b = number of blue marbles, and y = number of yellow marbles.

We can interpret the ratio of green to blue as:
$\frac{g}{b} = \frac{2}{7}$

We can write the number of blue marbles in terms of the number of green marbles:
$b = \frac{7}{2}g$

Interpret the ratio of green to yellow as:
$\frac{g}{y} = \frac{3}{5}$

We can write the number of yellow marbles in terms of the number of green marbles:
$y = \frac{5}{3}g$

The ratio of the number of blue marbles to yellow marbles is:
$\frac{b}{y} = \frac{\frac{7}{2}g}{\frac{5}{3}g} = \frac{7}{2} * \frac{3}{5} = \frac{21}{10}$

Since the ratio is more than 1, there are more blue marbles than yellow marbles.