Answer:
498.7 ft
Explanation:
The relation between time, speed, and distance can be used, along with a couple of units conversion factors.
Distance
The distance (d) covered at a rate (r) in time (t) will be given by ...
d = rt
The rate can be expressed in feet per second, so the units of distance come out in feet.
d = (17 mi/h)(5280 ft/mi)(1 h/(3600 s)) × (20 s)
= (17×5280×20)/3600 ft = 1496/3 ft ≈ 498.7 ft
The bicycle will travel about 498.7 feet in 20 seconds.
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Additional comment
The unit conversion factors are written such that the numerator and the denominator have the same value. The units of the conversion factor cancel the units you don't want and leave the units you do want.