Suppose that in a certain triangle, the degree measures of the exterior angles are in the ratio $2:3:4$. If the largest interior angle measures $y^\circ$, what is the value of $y$?

The exterior angles sum to 360^{o}, so if the "unit" exterior angle is x then 2x + 3x + 4x = 360 or x = 40^{o}. The smallest exterior angle is 2x = 80^{o}. So the largest interior angle is 180^{o} - 80^{o} = 100^{o}.