algebra
posted by Anonymous .
Machine A produces nails at a uniform rate of 60 every 20 seconds and machine B produces them at 50 every 10 seconds. If the two machines run simultaneously, how many seconds would it take to produce a total of 400 nails?

Rate of A = 60 nails / 20 sec = 3 nails/sec
rate of B = 50 nails / 10 sec = 5 nails/sec
combined rate = 8 nails/sec
time at combined rate = 400/8 seconds
= 50 seconds
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