Bunuel
Machine A, working alone at its constant rate, produces x pounds of peanut butter in 12 minutes. Machine B, working alone at its constant rate, produces x pounds of peanut butter in 18 minutes. How many minutes will it take machines A and B, working simultaneously at their respective constant rates, to produce x pounds of peanut butter?
A. 7
B. 7.2
C. 7.4
D. 7.5
E. 7.8
Another approach is to
assign a nice value to xLet's choose a value that works well 12 minutes and 18 minutes.
So, let's say x =
36Machine A, working alone at its constant rate, produces x pounds of peanut butter in 12 minutesIn other words, Machine A produces
36 pounds of peanut butter in 12 minutes
So, Machine A's RATE =
3 pounds per minute
Machine B, working alone at its constant rate, produces x pounds of peanut butter in 18 minutes. In other words, Machine B produces
36 pounds of peanut butter in 18 minutes
So, Machine B's RATE =
2 pounds per minute
How many minutes will it take machines A and B, working simultaneously at their respective constant rates, to produce x pounds (36 pounds) of peanut butter?COMBINED RATE =
3 pounds per minute +
2 pounds per minute =
5 pounds per minute
Time = output/rateSo, time =
36/
5 = 7.2 minutes
Answer: B
Cheers,
Brent