Bill can hammer 20 nails in 8 mins.Jeff can do the same job in only 5mins. How long will it take?

them to finish if Bill hammers the first 5 nails, then Jeff haammers for 3 minutes, then Bill finishes the job??


ANSWER IS 5.4 MINUTESBill can hammer 20 nails in 8 mins.Jeff can do the same job in only 5mins. How long will it take?
Ok you need some rates:





Let:


bR = rate at which bill hammers nails


jR = rate at which jeff hammers nails





bR = 2/5 minutes/nail


jR = 1/4 minutes/nail





Now to find the time:


1) Bill take 5 nails * 2/5 minutes/nail = 2 minutes to hammer 5 nails


2) If Jeff hammers for 3 minutes he will nail 12 nails


3) 20 - 17 = 3 nails it takes bill 2/5 minutes/nail = 6/5





total time I get is 6.2 minutesBill can hammer 20 nails in 8 mins.Jeff can do the same job in only 5mins. How long will it take?
Bill can hammer 5 nails in 2 mins (1/4th of number of nails %26amp; time taken)





Jeff can hammer 5 nails in 5/4 mins (1/4th of number of nails %26amp; time taken) = 1.25mins





So for 15 nails, Jeff takes 3*1.25 = 3.75


Total time = 2mins (Bill for 5 nails) %26amp; 3.75 (Jeff for rest of nails)


= 5.75
';Bill hammers the first 5 nails';


5 nails 脳 (8 minutes/20 nails) = 2 minutes





';Jeff hammers for 3 minutes';


3 minutes 脳 (20 nails/5 minutes) = 12 nails





';Bill finishes the job';


6 nails remaining


6 nails 脳 (8 minutes/20 nails) = 2.4 minutes





total time = 2 + 3 + 2.4


= 5.4 minutes