Answer:
18 ft/ 20 min = 0.90 ft/min is the greatest speed.
Explanation:
You must find the unit rate of change for all four items: A through D. This will require some conversion of units of measurement. Next you must determine which of your four results is the greatest / fastest.
A. 18 ft / 20 min = 9/10 ft/min, or 0.90 ft/min
B. 90 ft / 2.5 hr = 90 ft / 150 min = 6/10 ft/min, or 0.6 ft/min
C. 20 yd / 1.5 hr = 60 ft / 90 min = 6.7/10 ft/ min, or 0.67 ft/min
D. 3 2/3 yd / 15 min = (11/3)(3 ft) / 15 min = 7.3/10 ft /min, or 0.73 ft/min
Arranged in increasing size, we have:
6/10 ft/min, 6.7/10 ft/min, 7.3/10 ft/min and 9/10 ft/min.
The first answer choice, 9/10 ft/min, is the greatest speed.