Important information about Several algebra Word problems

Please see attachment.

82. Driving marathon. Felix drove 800 miles in x hours on
Monday.
a) Write a rational expression for his average speed.
b) On Tuesday he drove for 6 hours at the same average
speed. Write a rational expression for his distance on

90. Barn painting. Melanie can paint a certain barn by herself
in x days. Her helper Melissa can paint the same barn by
herself in 2x days. Write a rational expression for the fraction
of the barn that they complete in one day by working
together. Evaluate the expression for x _ 5.

64. Commuting students. At a well-known university, _
1
4 _
of the
undergraduate students commute, and _
1
3 _
of the graduate
students commute. One-tenth of the undergraduate students
drive more than 40 miles daily, and _
1
6 _
of the graduate
students drive more than 40 miles daily. If there are twice
as many undergraduate students as there are graduate
students, then what fraction of the commuters drive more
than 40 miles daily?

68
6.8 #36
36. Upstream, downstream. Junior's boat will go 15 miles per
hour in still water. If he can go 12 miles downstream in the
same amount of time as it takes to go 9 miles upstream,
then what is the speed of the current?

54. Big plane. A six-passenger plane cruises at 180 mph in
calm air. If the plane flies 7 miles with the wind in the
same amount of time as it flies 5 miles against the wind,
then what is the wind speed?

64. Filling a tank. A water tank has an inlet pipe and a drain
pipe. A full tank can be emptied in 30 minutes if the drain
is opened and an empty tank can be filled in 45 minutes
with the inlet pipe opened. If both pipes are accidentally
opened when the tank is full, then how long will it take to
empty the tank?