SOLUTION: PLease Help! Larry can destroy a room in 30 minutes, moe can destroy the same room in 40 minutes, but curly can destrot the room in 20 minutes. "working" together how long will

Question 22738: PLease Help!
Larry can destroy a room in 30 minutes, moe can destroy the same room in 40 minutes, but curly can destrot the room in 20 minutes. "working" together how long will it take them to destroy the poor room?
Found 2 solutions by venugopalramana, Earlsdon:
Answer by venugopalramana(3286) (Show Source): You can put this solution on YOUR website!
SEE THE FOLLOWING WHICH IS SIMILAR AND DO ACCORDINGLY.IN CASE OF DIFFICULTY PLEASE WRITE BACK

Please! If you could be so kind.
Question: If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?
The answer is suppose to be 2 hours and 24 minutes, but I can't seem to get the solution to it. Thank You.
1 solutions
Answer 10642 by venugopalramana(454) About Me on 2005-12-08 08:48:07 (Show Source):
I THINK I ANSWERED THIS QUESTION GIVING EXAMPLES.IF YOU HAVE NOT UNDERSTOOD IT,LET ME SOLVE..THE KEY IN THESE PROBLEMS IS TO FIND WORK DONE PER UNIT TIME FIRST FROM GIVEN DATA,COMBINE THEM AS REQUIRED AND THEN FIND THE TIME REQUIRED TO DO THE FULL JOB(THAT IS REVERSE THE FIRST STEP)WE HAVE....
SALLY CAN PAINT 1 HOUSE IN 4 HRS..SO IN 1 HR SHE CAN DO 1/4 HOUSE
JOHN CAN PAINT 1 HOUSE IN 6 HRS...SO IN 1 HR HE CAN PAINT 1/6 HOUSE...
SO TOGETHER THEY CAN PAINT 1/4 +1/6 HOUSE IN 1 HR =(3+2)/12 HOUSE IN 1 HR.=5/12 HOUSE IN 1 HOUR....
SO FULL HOUSE THEY CAN PAINT IN 1/(5/12)=12/5=2.4 HRS.=2HRS AND 0.4*60=24 MTS.OR 2HRS 24 MTS. TIME.
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Try this:
If Larry can destroy the room in 30 minutes, he can destroy 1/30 of the room in 1 minute.
If Moe can destroy the room in 40 minutes, he can destroy 1/40 of the room in 1 minute.
If Curly can destroy the room in 20 minutes, he can destroy 1/20 of the room in 1 minute.
So, together, they can destroy of the room in 1 minute.
Therefore, it will take them minutes to destroy the room working together.
minutes = 9 minutes and 13.8 seconds.
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