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| Math Central | Quandaries & Queries |
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Question from David, a student: Della can scrape the barnacles from a 70 ft. yacht in 10 hours using an electric barnacle scraper. Don can do the same job in 15 hours using a manual scraper. If Della started helping Don three hours after Don started scraping, how long will it take to scrape the entire boat? Well i know that to do for this problem, but with that start helping at 3 hours after Della have already began working i don't know how to set this up correctly could you please show me how? thanks |
Hi David,
Della can scrape the ship in 10 hours so she scrapes at the rate of one tenth of a ship per hour. She works for 3 hours so she scraped three tenths of the ship.
Della can scrape a ship in 10 hours and Don can scrape a ship in 15 hours. If they work together how long does it take to scrape seven tenths of a ship?
Penny
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