Answer:
Therefore the number of brown shells in each necklace was = 2 brown shells.
Step-by-step explanation:
If Julie made identical necklaces then we can say that number of each different colored shells were equally distributed among the necklaces.
So we can say that to find the number of necklaces we have to find the GCD (greatest common denominator) of the different colored shells.
Therefore the GCD of 10, 15 and 20 is 5.
Therefore Julia made 5 necklaces.
Therefore the number of brown shells in each necklace was = = 2 shells.