Question 57
<pre><font face = "courier new"><b>>>...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
<font size = 4 color = "blue">TOTAL TIME = 100/x + 200/(x-20)</font>
>>...Evaluate the expression if x=100...<<
TOTAL TIME = 100/100 + 200/(100-20)
           = 1 + 200/80
           = 1 + 2.5 
           = <font color = "blue" size = 4>3.5 hours.

Edwin <font face = "wingdings" size = 7 color = "red">J</font