SOLUTION: Hello, I am having trouble solving this word problem. I tried 1/8 + 1/12 = 1/x The problem is: Batman can clean up all of the crime in Gotham City in 8 hr working alone. R

Question 338694: Hello,
I am having trouble solving this word problem. I tried 1/8 + 1/12 = 1/x
The problem is:
Batman can clean up all of the crime in Gotham City in 8 hr working alone. Robin can do the same job alone in 12 hr. 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 8 hr working alone.
Robin can do the same job alone in 12 hr.
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 = crime fighting time of Robin
then
(t-2) = crime fighting time for Batman who started 2 hrs later
:
Let the completed job = 1 (a crime free city)
:
A shared work equation
+ = 1
Multiply by 24 to clear the denominators, results:
2t + 3(t-2) = 24
2t + 3t - 6 = 24
5t = 24 + 6
5t = 30
t =
t = 6 hrs is Robin's crime fighting time
therefore
8AM + 6 = 2PM it will free of crime!!!
:
:
Check this, (Batman works only 4 hrs)
+ = 1
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