SOLUTION: Jeremy and his dad can wash his car together in 40 minutes, Jeremy can wash it by himself in 70 minutes. How long would it take his dad to wash it by himself?

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Question 751337: Jeremy and his dad can wash his car together in 40 minutes, Jeremy can wash it by himself in 70 minutes. How long would it take his dad to wash it by himself?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of washing to get their rate
working together
Let +t+ = minutes for Dad to wash car
( 1 car / 70 min ) + ( 1 car / t min ) = ( 1 car / 40 min )
+1+%2F70+%2B+1%2Ft+=+1%2F40+
Multiply both sides by +280t+
+4t+%2B+280+=+7t+
+3t+=+280+
+t+=+93.+333+
+93.333+-+60+=+33.333+
Dad will take 1 hour 33 min and 20 sec
check:
+1+%2F70+%2B+1%2Ft+=+1%2F40+
+1+%2F70+%2B+1%2F93.333+=+1%2F40+
+.0142857+%2B+.0107143+=+.025+
+.025+=+.025+
OK