Questions on Mileage and Lake Depth

1.
Gas mileage actually varies slightly with the driving speed of a car (as well as with highway vs. city driving). Suppose your car averages 35 miles per gallon on the highway if your average speed is 50 miles per hour, and it averages 27 miles per gallon on the highway if your average speed is 69 miles per hour. Answer parts (a) and (b) below.

a. What is the driving time for a 3100-mile trip if you drive at an average of 50 miles per hour? What is the driving time at 69 miles per hour?

The driving time at 50 miles per hour is ___ hours.
(Type an integer of decimal rounded to two decimal places as needed.)

The driving time at 69 miles per hour is ___ hours.
(Type an integer of decimal rounded to two decimal places as needed.)

b. Assume a gasoline price of $4.85 per gallon. What is the gasoline cost for a 3100-mile trip if you drive at an average speed of 50 miles per hour? What is the gasoline cost at 69 miles per hour?

The gasoline cost at 50 miles per hour is $___
(Round to two decimal places as needed.)

The gasoline cost at 69 miles per hour is $___
(Round to two decimal places as needed.)

2.
A lake in a certain country has a volume of approximately 2659 cubic kilometers, and its surface area is 69,380 square kilometers. Complete parts (a) through (c) below

a. What is the average depth of the lake (the depth of a box with the volume and surface of the lake )?

___ km
(Round to three decimal places as needed.)

b. In the past six years, the water level of the lake has dropped 12 feet from the depth computed in part (a). Approximately how much water has the lake lost?

Therefore, the lake lost ___ km3 of water.
(Round to the nearest whole number as needed.)

c. What percentage of the volume has been lost?

The percentage of volume that has been lost is ___%
(Round to the nearest whole number as needed.)