SOLUTION: Batman can clean up all of the crime in Gotham city in 8hr working alone. Robin can do the same job alone in 12hr. If Robin starts crime fighting at 8 A.M. and Batman joins him a

Question 122330: Batman can clean up all of the crime in Gotham city in 8hr working alone. Robin can do the same job alone in 12hr. If Robin starts crime fighting at 8 A.M. and Batman joins him at 10 A.M.. then at what time will they have all of the crime cleaned up?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Batman can clean up all of the crime in Gotham city in 8hr working alone. Robin can do the same job alone in 12hr. If Robin starts crime fighting at 8 A.M. and Batman joins him at 10 A.M.. then at what time will they have all of the crime cleaned up?
:
Let t = time spent by Batman to wipe out crime
then
(t+2) = time spent by Robin to wipe out crime
:
Let the completed job = 1
:
+ = 1
:
Multiply equation by 24 to get rid of the denominators
24* + 24* = 24(1)
Cancel out the denominators and you have:
:
3t + 2(t+2) = 24
:
3t + 2t + 4 = 24
:
5t = 24 - 4
t =
t = 4 hrs Batman's time which started at 10 AM, therefore
Completed job will be at 2 PM
:
:
Check solution:
+ = 1; confirms our solution

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