candygal79 wrote:A metal company's old machine makes bolts a constant rate of 100 bolts per hour. The company's new machine makes bolts constant rate of 150 bolts per hour. If both machine start at the same time and continue making bolts simultaneously, how many MINUTES will it take the two machines to make a total of 300 bolts ?
A 36
B 72
C 120
D 144
E 180
Rates are ADDITIVE.
When the two machines work together, their combined rate = 100+150 = 250 bolts per hour.
Time for the two machines to produce 300 bolts = w/r = 300/250 = 6/5 hours.
Since 1 hour = 60 minutes, we multiply by 60 to convert hours to minutes:
(6/5) * 60 = 72 minutes.
The correct answer is
B.
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