Answer:
20 miles per hour
Explanation:
The graph shows it takes Colin 45 minutes (3/4 hour) to drive home. For a given distance (the distance from home to market), the speed is inversely proportional to the time.
The time driving home is (3/4 hour)/(2/4 hour) = 3/2 times the time driving to the market. The inverse of this is 2/3, so Colin's speed driving home is ...
(2/3)(30 mph) = 20 mph
The speed at which Colin drives home is 20 miles per hour.
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Alternate solution
The distance to the market is ...
distance = speed × time
distance = (30 mi/h)(1/2 h) = 15 mi
The speed going home is ...
speed = distance/time
speed = (15 mi)/(3/4 h) = (15)(4/3) mi/h = 20 mi/h