She can use 12 jewels for each pair of jeans. In fact, using 12 jewels per jeans implies that she will use [tex] 12 \cdot 4 = 48 [/tex] jewels. The two remaining jewels can't be used on any pair of jeans, otherwise she wouldn't use the same number of jewels for each jeans.
This derives from the fact that, if you divide 50 by 4, you get a result of 12 with a remainder of 2.
