Working simultaneously and independently at an identical constant rate, 5 machines of a certain type can produce a total of x units of product P in 8 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?  Pick.
A) 30	B) 18	C) 16	D) 12	E) 8
5 machines do x units in 8 days   we have x/8 =&gt; rate of the 5 machines   we know that we need to have 3x units in 4 days   therefore, we need to get to 3x/4 rate of the machines.   rate of one machine is x/8*1/5 = x/40.   now, we need to know how many machines need to work simultaneously, to get 3x done in 4 days.   3x/4 work needs to be done by machines that work at x/40 rate.   let's assign a constant Y for the number of machines:   (x/40)*y = 3x/4   y = 3x/4 * 40/x   cancel 4 with 40, and x with x and get -&gt; 30. 30nswer choice 30
<result>A</result>
Working simultaneously and independently at an identical constant rate, 5 machines of a certain type can produce a total of x units of product P in 8 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?