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Explanation:
1/6 cup of glitter is needed for each 1/3 cup of glue. We want that "1/3 cup of glue" to be "1 cup of glue". So we'll multiply each part by 3.
The ratio 1/6 : 1/3 updates to 1/2 : 1 to tell us that we need 1/2 cup of glitter to pair with 1 cup of glue.