SOLUTION: Fred can seal asphalt driveway in 1/3 the time it takes John. Working together, it takes them 1 1/2 hours. How long would it have taken Fred working alone?

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Question 1191073: Fred can seal asphalt driveway in 1/3 the time it takes John. Working together, it takes them 1 1/2 hours. How long would it have taken Fred working alone?
Found 3 solutions by josgarithmetic, ikleyn, greenestamps:
Answer by josgarithmetic(39618)   (Show Source): You can put this solution on YOUR website!
If the time for Fred working alone for the job is , the the time for John working alone is . Both working together, time hours.


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Answer by ikleyn(52788)   (Show Source): You can put this solution on YOUR website!
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Fred can seal asphalt driveway in 1/3 the time it takes John.
Working together, it takes them 1 1/2 hours. How long would it have taken Fred working alone?
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            This problem can be solved  MENTALLY,  without using equation,
            by applying reasoning and common sense. 


The problem says that Fred works as productive, as 3 instanses of John.


Next, the problem says that working together, they complete the job in 1.5 hours.


It is the same as to say that 4 instances of John will complete the job in 1.5 hours.


Hence, John alone will do the job in 4*1.5 = 6 hours.


It implies that Fred, working 3 times as fast as John, will complete the job in 6:3 = 2 hours.    ANSWER

Solved     //     mentally.



Answer by greenestamps(13200)   (Show Source): You can put this solution on YOUR website!


Another mental solution that gives you good mental exercise....

Since Fred takes 1/3 as long as John to do the job, when they work together Fred does 3/4 of the work while John does 1/4.

Since it take them 1 1/2 hours to do the job together, that means Fred does 3/4 of the job in 1 1/2 hours; and that means it would take him 4/3 times 1 1/2 hours, or 2 hours, to do the job alone.

ANSWER: 2 hours
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