Math CentralQuandaries & Queries


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?


About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS