SOLUTION: How many days will 1200 persons take to construct a bridge, if 450 persons can build the same in 45 days?

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Question 886201: How many days will 1200 persons take to construct a bridge, if 450 persons can build the same in 45 days?
Answer by Edwin McCravy(20062)   (Show Source): You can put this solution on YOUR website!

Two ways to work it.

First way:

The LCM of 1200 persons and 450 persons is 3600 persons.

3600 persons is 3 times as many persons as 1200 persons and
3600 persons is 8 times as many persons as 450 persons.

Since 450 persons can build 1 bridge in 45 days, then 

3600 persons can build 8 bridges in 45 days.

So only 1200 persons will take 3 times as long or 135 days to build 8 bridges.

So to build only 1 bridge it will take 1200 persons only 1/8th as long,
and
1/8th of 135 days is 135/8 =  days.

------------------------------------------------------

Second way:

You can also use the worker-time-job formula, which is:



where

W1 = the number of workers in the first situation.
T1 = the number of time units (days in this case) in the first situation.
J1 = the number of jobs in the first situation.

W2 = the number of workers in the second situation.
T2 = the number of time units (days in this case) in the second situation.
J2 = the number of jobs in the second situation.

W1 = 1200             W2 = 450     
T1 =  ? (unknown)     T2 = 45
J1 =  1               J2 = 1









Reduce that fraction by dividing numerator and
denominator by 150



 days

Edwin
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