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Unformatted text preview: pent ö æ Work Rate öæ Time Spent ö
ç
÷ç
÷+ç
÷ç
÷ =1
è of Mary øè Working ø è of John øè Working ø
This time we know that the time spent working together is 3.5 hours. We now need to find the
work rates for each person. We’ll start with Mary. 1 Job = ( Work Rate of Mary ) ´ ( 5 ) Þ Work Rate of Mary = 1
5 Now we’ll find the work rate of John. Notice however, that since we don’t know how long it will
take him to do the job by himself we aren’t going to be able to get a single number for this. That
is not a problem as we’ll see in a second. 1 Job = ( Work Rate of John ) ´ ( t ) Þ Work Rate of John = 1
t Notice that we’ve managed to get the work rate of John in terms of the time it would take him to
do the job himself. This means that once we solve the equation above we’ll have the answer that
we want. So, let’s plug into the work equation and solve for the time it would take John to do the
job by himself. 1
1
( 3.5) + ( 3.5 ) = 1
5
t
3.5t + ( 3.5)( 5 ) = 5t Multiplying both sides by 5t 17.5 = 1.5t
17.5
=t...
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 Spring '12
 MrVinh

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