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Question 54600: It takes 5 hours for John to do some job. he worked for an hour , and then Mike joined . Together they finished the job in 1 1/2 hour.
a) how long would it take mike to do the job by himself?
b) if john worked for 3 hours before mike joined him , how long would it take for them to finish the job together?
Answer by venugopalramana(3286)   (Show Source):
You can put this solution on YOUR website! It takes 5 hours for John to do some job.
JOHN IN 1 HR DOES 1/5=0.2 JOB
he worked for an hour ,
HENCE JOHN COMPLETED 1/5 JOB....
BALANCE JOB = 1-1/5 = 4/5=0.8 JOB
and then Mike joined . Together they finished the job in 1 1/2 hour.
THAT IS JOHN + MIKE TOOK 1.5 HRS TO DO 4/5=0.8 JOB
JOHN+MIKE DO IN 1 HR 0.8/1.5=8/15 JOB
BUT JOHN DOES IN 1 HR 1/5 JOB
SO MIKE DID IN 1 HR .....8/15 - 1/5 = 5/15=1/3 JOB
SO MIKE NEEDS 1/(1/3) HRS = 3 HRS TO DO 1 WHOLE JOB.
a) how long would it take mike to do the job by himself?
SO MIKE NEEDS 1/(1/3) HRS = 3 HRS TO DO 1 WHOLE JOB.
b) if john worked for 3 hours before mike joined him , how long would it take for them to finish the job together?
JOHN DOES IN 3 HRS 3/5 JOB
BALANCE JOB =1-3/5 = 2/5 JOB
JOHN + MIKE DO IN 1 HR 8/15 JOB
JOHN + MIKE NEED (2/5)/(8/15)=(2*15)/(8*5) = 3/4 HRS TO COMPLETE THE JOB
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