if 6 machines do it at the same rate and finish in 12, then find the rate that one machine can do this on its own.

6/m=12, then m=72 days per machine , the rate one machine can do the job.

then 72/8 gives the machines you need to finishin 8 days, which is 9.



the additional machines are 9-6=3.
can someone double check my work? tks

3 is the correct answer

Sorry but I still dint get the catch here!! Can somebody pls explain in an easier way??

It looks like freesl meant to write m/6 = 12, and m = 72.

If it takes one machine 72 days to finish the job then how many machines will you need in order to finish the job in 8 days?

In other words, to how many machines do you need to distribute the work in order to cut the total work from 72 days to 8 days. Therefore:

72/8 = 9

It takes 9 machines to complete this job in 8 days, compared to 1 machine completing the job in 72 days, or 6 machines completing it in 12 days.

Since you already have 6 machines, you need 3 additional machines to make it 9 machines total.

Think of it this way.

There is a job that needs to be done. The job takes 72 days. To how many machines would you have to distribute this job in order to cut it down from 72 days to 8 days. That is why you have to divide 72 days (the job) by the number of days/hours in which you would like to finish the job.

8*n/ 72 = 12*6/72

n = number of machines taken to complete the task in 8 days.
Rate = 72 days per machine