kiseki wrote:
Three machines operating independently, simultaneously, and at the same constant rate can fill a certain production order in 36 hours. If one additional machine were used under the same operating conditions, in how many fewer hours of simultaneous operation could the production order be fulfilled?
A. 6
B. 9
C. 12
D. 27
E. 48
Use unitary method...
Take total work = 1
3 machines take 36 hours to complete the entire work = 1
1 machine take 36 hours to complete = 1/3 work
1 machine take 1 hour
...
