SOLUTION: Working alone two metal crushers can each process one truckload of aluminum cans in 25 min. After the two machines have been working for 6 min they are joined by a third machine th

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Question 391276: Working alone two metal crushers can each process one truckload of aluminum cans in 25 min. After the two machines have been working for 6 min they are joined by a third machine that by itself could process one truckload in 20 min. How long after the first two machines start working will one truckload of cans be processed?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
each machine does a FRACTION of the job , based on the individual times ___ the fractions add to one (the WHOLE job)

(x / 25) + (x / 25) + [(x - 6) / 20] = 1

multiplying by 100 (LCD) ___ 4x + 4x + 5x - 30 = 100