Of all the players in a professional baseball league, 1/2

There are 4 main approaches to solve overlapping sets problem:
1. Pure logic and simple math;
2. Direct formulas (check the following link for the formulas of 3 overlapping sets: formulae-for-3-overlapping-sets-69014.html#p729340);
3. Venn diagram (check this: how-to-draw-a-venn-diagram-for-problems-98036.html);
4. Double-set matrix.

It depends on the problem, as well as on one's personal preferences to pick which approach to apply to some particular problem.

Also notice that when there are some percents and ratios involved, it's almost always a good idea for plug-in method.

For example, for this problem I'd use double-set matrix method along with plug-in method. Pick some smart number for total players, so that all subsets will be integers: as there are 1/2, 1/3 and 3/4 involved pick 12 (the lowest common denominator). Next, fill the matrix step by step:Question asks: what percentage of the players who are not pitchers are foreign-born? So basically we need the ratio of yellow cells, which is 3/3=1, so the answer is 100%.

Answer: A.

Hope it helps.