Answer:
6 machines
Step-by-step explanation:
Let x be the time needed for 1 machine to complete the job, so rate of one machine is (rate is the reciprocal of time)
[tex] \frac{1}{x} [/tex]
rate of 4 machines would be
[tex]1 \: job = 12 \times \frac{4}{x} = \frac{48}{x} \\ 1 \: macine \: takes \: 48 \: days[/tex]
[tex] \frac{48 \: days \: per \: machine}{8 \: days} = 6 \: machines[/tex]
