In a nuts and bolts factory, one machine produces only nuts at the rate of 100 nuts per minute and needs to be cleaned for 5 minutes after production of every 1,000 nuts. Another machine produces only bolts at the rate of 75 bolts per minute and needs to be cleaned for 10 minutes after production of every 1,500 bolts. If both the machines start production at the same time, what is the minimum duration required for producing 9,000 pairs of nuts and bolts?
Pick one.
A) 130 minutes  B) 135 minutes  C) 170 minutes  D) 180 minutes  E) 190 minutes
Total number of nuts produced in 10 minutes = 1000.   An extra 5 minutes is required to clean those nuts.   Thus, the total time required in producing 1000 nuts = 15 minutes.   Now, total number of bolts produced in 20 minutes = 1500.   Here also an extra 10 minutes is required to clean those bolts.   Thus, the total time required in producing 1500 bolts = 30 minutes.   Also, 2000 nuts will be produced in 30 minutes. Hence, the rate of production of nuts is greater than the rate of production of bolts.   Thus, in order to determine the minimum duration required for producing 9,000 pairs of nuts and bolts, we only need to determine the time required for producing 9000 bolts.   Hence, the time required for producing 9000 bolts = (9000 x 30)/ 1500 = 180 minutes   ANSWER:180 minutes
<result>D</result>
In a nuts and bolts factory, one machine produces only nuts at the rate of 100 nuts per minute and needs to be cleaned for 5 minutes after production of every 1,000 nuts. Another machine produces only bolts at the rate of 75 bolts per minute and needs to be cleaned for 10 minutes after production of every 1,500 bolts. If both the machines start production at the same time, what is the minimum duration required for producing 9,000 pairs of nuts and bolts?