>>...After leaving Moose Jae, Hanson drove 100 kilometers at 

x km/hr and then decreased his speed by 20 km/hr and drove 

another 200 additional kilometers. Write a rational expression 

for his total traveling time.<< 



Use TIME = DISTANCE/SPEED



>>...drove 100 kilometers at x km/hr...<<



Translation: TIME to travel the 100 kilometers = DISTANCE/SPEED

or 100/x

 

>>...decreased his speed by 20 km/hr and drove another 200 

additional kilometers...<<



Translation: He decreased his speed from x km/hr to (x-20) km/hr

So the TIME for the 200 additional kilometers = DISTANCE/SPEED

or 200/(x-20)



So:



Total TIME = TIME to travel the 100 km + TIME to travel the 200 km

TOTAL TIME = 100/x + 200/(x-20)

>>...Evaluate the expression if x=100...<<

TOTAL TIME = 100/100 + 200/(100-20)

           = 1 + 200/80

           = 1 + 2.5 

           = 3.5 hours.



Edwin J

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