math challenge

Weeks of March 2 - 15, 1998

Gemstones for Ms. Iva Gotmoni

Ms. Iva Gotmoni was visiting her favourite jewelry store when she noticed four new necklaces in the center showcase.

A sales person notices Iva's fascination with the sparkling blue, green and black gemstones in the necklaces. She shows Iva the necklaces and tells her:

"Each blue gemstone is worth twice as much as each green gemstone. While each black gemstone is worth twice as much as each blue gemstone. But oddly enough, each necklace is still worth the value of four blue gemstones."

There are 20 gemstones altogether. If each necklace is different, what colored gemstones are in each necklace?

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