A unit rate is a comparison of two different quantities with a denominator of one. Here are the descriptions you provided and whether they represent unit rates:
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100 calories for 2 servings - This is not a unit rate. It can be simplified to 50 calories per serving.
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$5 for every pound - This is a unit rate. It represents $5 per pound.
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1 mile per 3 hours - This is not a unit rate. It can be simplified to \( \frac{1}{3} \) miles per hour.
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4 words per minute - This is a unit rate, representing 4 words in 1 minute.
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$2 for every 30 minutes - This is not a unit rate. It can be simplified to \( \frac{2}{30} \) dollars per minute or \( \frac{1}{15} \) dollars per minute.
Based on this analysis, the rate descriptions that represent unit rates are:
- $5 for every pound
- 4 words per minute