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George can mow his lawn in 3 hours, Al can mow his lawn in 5 hours.  How long will it take both of them working together?

 Feb 29, 2020
 #1
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1/3   +   1/5     =    1/B       B is the time for Both working (in hours)   Solve for B

 Feb 29, 2020
 #2
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George can mow his lawn in 3 hours, Al can mow his lawn in 5 hours.  How long will it take both of them working together? 

 

We're assuming George's lawn and Al's lawn are the same size, to make 

the rates consistent, and that they're working together on the same lawn. 

 

George's rate of mowing is 1 lawn per 3 hours, which is 1/3 lawn/hour. 

Al's          rate of mowing is 1 lawn per 5 hours, which is 1/5 lawn/hour. 

 

Working together means add the two rates    1/3 + 1/5  =  combined rate of mowing 

 

After finding common denominator                5/15 + 3/15  =  8/15     They can mow 8 lawns in 15 hours. 

 

So 8/15 lawns per hour ... invert that amount to get the value in units of hours per lawn 

 

15/8 hours per lawn, which when you do the division is 1.875 hrs/lawn,

or another way of saying it is:  one hour, fifty-two & a half minutes

.

 Feb 29, 2020
 #3
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So basically 1:52:30

AnimalMaster  Feb 29, 2020

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