
Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion 
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February 18th, 2019, 11:01 AM  #1 
Newbie Joined: Feb 2019 From: Britain Posts: 2 Thanks: 0  Gas Tanks!
Lucy find out that a block of sodium reacts with oxygen in a tank and exhausts the supply of oxygen in 3 minutes. Potassium does this same thing in 4 minutes and magnesium takes 6 minutes. How long would it take to use up all the oxygen in the tank if one block of each of the three metals were placed inside simultaneously? (The assumption is that the reactions don't affect one another.)

February 18th, 2019, 11:53 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,122 Thanks: 1003 
Look at it as a time = distance/speed problem: S................................1................ ..............>3 min P................................1................ ..............>4 min M...............................1................. ..............>6 min S+P+M.......................1..................... ..........>x min ? S speed = 1/3, P speed = 1/4, M speed = 1/6 x = 1 / (1/3 + 1/4 + 1/6) Continue... 