Problem of the Week
Problem C
Marbles, Marbles

A box contains $6$ red marbles, $5$ blue marbles, $2$ yellow marbles, and $3$ green marbles. Several orange marbles are added to the box. All the marbles in the box are identical except for colour.

A marble is then randomly selected from the box, and the probability that a blue or green marble is selected is $\frac{2}{7}$.

How many orange marbles were added to the box?

Themes: Algebra, Data Management