Blue Beaded

How many ways are 5 blue balls 4 green beads and 3 red beads are strung on one line?

I do not understand how this kind of probabilities Question

in (5 +4 +3)! / {(5!) * (4!) * (3!)} = 27 720 ways in a row and 27720 / 2 = 13 860 ways in a string form a necklace.

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