A sweater is marked down from $25 to $18. What is the percent of change
2 answers:
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If Ann cleans in 12 hours then she cleans 
of the apartment per hour. Similarly Liz cleans 
of the appartment per hour. So together then can clean 
of the apartment for hour. Therefor it will take them 
hours to clean.
The general formula
can be used as a check if needed.
The general formula