Working simultaneously and independently at an identical constant rate, 6 machines of a certain type can produce a total of x units of product P in 10 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 5x units of product P in 6 days?
Pick:
A) 50  B) 18  C) 16  D) 12  E) 8

Rationale: "6 machines do x units in 10 days we have x / 10 = > rate of the 6 machines we know that we need to have 5 x units in 6 days therefore , we need to get to 5 x / 6 rate of the machines . rate of one machine is x / 10 * 1 / 6 = x / 60 . now , we need to know how many machines need to work simultaneously , to get 5 x done in 6 days . 5 x / 6 work needs to be done by machines that work at x / 60 rate . let ' s assign a constant y for the number of machines : ( x / 60 ) * y = 5 x / 6 y = 5 x / 6 * 60 / x cancel 6 with 60 , and x with x and get - > 50 . answer choice a"
Answer: A