If the two of you can wash 1 car in 6 minutes:
It will take you 10 minutes to wash the car alone
take your friend 15 minutes to wash the car alone
Let the duration you can work be represented by y
Let the duration your friend can work be represented by x
You can wash a car 1.5 times as fast as your friend
That is, y = 1.5x
Working together, the two of you can wash 1 car in 6 minutes
This can be represented by the equation
Substitute x = 1.5y into the equation above
It will take you 10 minutes to wash the car alone
Substitute y = 10 into x = 1.5y
x = 1.5(10)
x = 15 minutes
It will take your friend 15 minutes to wash the car alone
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