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A man can clear his driveway using a snowblower in 45 minutes. It takes his son 2 hours to clear the driveway using a shovel. About how long would it take them to clear the driveway if they worked together?

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Greenleafable
Father's rate: 1/45 (driveways/minute)
Son's rate: 1/120 (driveways/minute: 2 hours equals 120 minutes)
combined rate: 1/45 + 1/120 = 11/360 (driveways/minute)

time at combined rate: 1/(11/360) = 
360/11 minutes =
32.73 minutes, which is about 33 minutes

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