Emily bought 9 packs of candy necklaces * 8 candy necklaces in a pack = <<9*8=72>>72 candy necklaces.
Her classmates took 72 candy necklaces – 40 candy necklaces left = <<72-40=32>>32 candy necklaces
Since each pack contained 8 necklaces, this means 32 / 8 = <<32/8=4>>4 packs of candy necklaces were opened.
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