Alex drove 18 kilometers at a constant speed. If he had driven 30 kilometers per hour faster, he would have traveled the same distance for 48 minutes less. How fast did he drive?

Answer 1

d= 18 km

at x km/hr =kph

d=rt, distance = rate of speed times time traveled

18 = rt

18= (r+30)(t-48) = (r+30)(t-4/5)

original speed = 15 kph and time = 1.2 minutes = 1 minute and 12 seconds

at 30 kph faster, new speed = 45 kph and new time = .4 minutes = 24 seconds

two equations two unknowns

use substitution, elimination, r=15, t= 6/5 hours. convert 48 minutes to 4/5 hours

18 = 15(6/5) =3x6

18 = (15+30)(6/5-4/5) = 45(2/5) = 9x2

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