SOLUTION: Danna can wash 15 dishes in 15 minutes while Dave can wash the same number of dishes for 25 minutes. How long will they be able to finish washing 15 dishes if they work together?

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Question 994156: Danna can wash 15 dishes in 15 minutes while Dave can wash the same number of dishes for 25 minutes. How long will they be able to finish washing 15 dishes if they work together?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Since they only talk about 15 dishes, I
will say: 15 dishes = 1 job
Dana's rate of washing is:
+1%2F15+ job/min
Dave's rate of washing is :
+1%2F25++ jobs/min
-----------------------
Let +t+ = minutes to wash 15 dishes
when they work together
+1%2F15+%2B+1%2F25+=+1%2Ft+
Multiply both sides by +75t+
+5t+%2B+3t+=+75+
+8t+=+75+
+t+=+9.375+ min
+.375%2A60+=+22.5+
It will take them 9 min 22.5 sec working together
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check:
+1%2F15+%2B+1%2F25+=+1%2Ft+
+1%2F15+%2B+1%2F25+=+1%2F9.375+
+.0667+%2B+.04+=+.10667+
+.1067+=+.10667+
OK