Answer:
12 minutes
Step-by-step explanation:
Candles can be manually packed at the rate of ...
... (400 candles)/(36 minutes) = 11 1/9 candles/minute
The two systems together pack candles at the rate of ...
... (400 candles)/(9 minutes) = 44 4/9 candles/minute
Then the machine's packing rate is the difference between the total and the manual rates:
... machine rate = (44 4/9 candles/minute) - (11 1/9 candles/minute)
... = 33 1/3 candles/minute.
At this rate, the machine working alone can pack 400 candles in ...
... (400 candles)/(33 1/3 candles/minute) = (400/(100/3)) minutes
... = 400 × 3/100 minutes = 12 minutes
