m men can build a wall in d days. how many days will n men take to build the same wall?
Variables are:
m = number of men for a defined job
d = number of days for the defined job
n = number of men different than m, .
CALCULATE THE WORK RATE FOR ONE MAN.
The defined group of men need d number of days, so if only 1 man is available, he needs m times as many days to do the job. This means the one-man rate is 1 man needs days.
His rate can be expressed as jobs per day.
RATE FOR A DIFFERENT NUMBER OF MEN.
Now, you want the rate for some other number of men; the quantity, n men. What is the rate now if n men are to do the job? The rates are additive, so each man in the group contributes at 1/(d*m) jobs per day; and since we now have n men to do this job, the rate is: jobs per day.
In your actual question you can find the given variables' values and just substitute them into the expression:
m=12; d=4; n=3. jobs per day
That means 16 days needed for the 3 men to do the job of building this wall.
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