chickenpatty Posted February 8, 2012 Share Posted February 8, 2012 If it takes Bob 4 hours to complete a job, and it takes Sally 6 hours to do the same job, how long will it take if they both work together? How do you figure this out? Can someone 'splain it to me? Quote Link to comment Share on other sites More sharing options...
k2bdeutmeyer Posted February 8, 2012 Share Posted February 8, 2012 average?? I dunno! Quote Link to comment Share on other sites More sharing options...
arstephia Posted February 8, 2012 Share Posted February 8, 2012 I guess it would take 8 hours because Bob will sit back with his i-phone while Sally complains for 2 hours about Bob not helping her before she finally just gets fed up and does it by herself. :lol: Quote Link to comment Share on other sites More sharing options...
LinRTX Posted February 8, 2012 Share Posted February 8, 2012 This is a rate problem. Rate x time = job. Bob's rate is 1 job/4hours. Sally's rate is 1 job/6hours. Together : Bob's rate x time for job + Sally's rate x time for job = job (1 job/4 hours) x time + (1 job/6 hours) x time = 1 1/4 t + 1/6 t = 1 Finding common denominators: 3/12 t + 2/12 t =1 5/12 t = 1 t = 12/5 = 2.4 hours Does that make sense? Linda Quote Link to comment Share on other sites More sharing options...
thescrappyhomeschooler Posted February 8, 2012 Share Posted February 8, 2012 This is a rate problem. Rate x time = job. Bob's rate is 1 job/4hours. Sally's rate is 1 job/6hours. Together : Bob's rate x time for job + Sally's rate x time for job = job (1 job/4 hours) x time + (1 job/6 hours) x time = 1 1/4 t + 1/6 t = 1 Finding common denominators: 3/12 t + 2/12 t =1 5/12 t = 1 t = 12/5 = 2.4 hours Does that make sense? Linda This makes sense, but I like this answer better: :lol: I guess it would take 8 hours because Bob will sit back with his i-phone while Sally complains for 2 hours about Bob not helping her before she finally just gets fed up and does it by herself. :lol: Quote Link to comment Share on other sites More sharing options...
chickenpatty Posted February 8, 2012 Author Share Posted February 8, 2012 Ahh, thank you so much! Quote Link to comment Share on other sites More sharing options...
chickenpatty Posted February 8, 2012 Author Share Posted February 8, 2012 I guess it would take 8 hours because Bob will sit back with his i-phone while Sally complains for 2 hours about Bob not helping her before she finally just gets fed up and does it by herself. :lol: :lol: Quote Link to comment Share on other sites More sharing options...
Onceuponatime Posted February 8, 2012 Share Posted February 8, 2012 (edited) . Edited February 8, 2012 by Onceuponatime Quote Link to comment Share on other sites More sharing options...
Sophia Posted February 8, 2012 Share Posted February 8, 2012 Chapter 1 of Becoming a Problem Solving Genius by Zaccaro covers problems like this. His explanations are what finally helped me make sense of problems like these. Fwiw :001_smile: Quote Link to comment Share on other sites More sharing options...
Dana Posted February 8, 2012 Share Posted February 8, 2012 If it takes Bob 4 hours to complete a job, and it takes Sally 6 hours to do the same job, how long will it take if they both work together? How do you figure this out? Can someone 'splain it to me? I think the most common error is when people average the times and say 5 hours. The trick to avoiding this mistake is to realize that if Sally heads out and goes shopping, the job will be done in 4 hours by Bob, so if they're working together (and not getting in each other's way) the job will be done in LESS time than it would take the fastest one alone. (It's not like when a child helps you with a household chore.) Quote Link to comment Share on other sites More sharing options...
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