Answer:
6
Step-by-step explanation:
The greatest common factor of 72 and 42 is 6. From this, we can tell that the highest number of friends to receive a necklace is 6. The total beads can also be divided to get the amount on each necklace.
72 / 6 = 12
42 / 6 = 7
So, each necklace would have 12 blue beads and 7 red beads, making 6 necklaces.