Answer:
a) 48 gigabytes
b) 250 minutes, or 4 hours 10 minutes
Explanation:
For D(t) = 75 -0.3t modeling the number of remaining gigabytes to download after t minutes, you want to find D(90) and t such that D(t) = 0.
a) Remaining
D(90) = 75 -0.3·90 = 48
After 90 minutes, 48 gigabytes are left to download.
b) Total time
The time required to complete the entire download is given by ...
0 = 75 - 0.3t
0 = 250 -t . . . . . divide by 0.3
t = 250 . . . . . . add t
It will take 250 minutes, or 4 hours 10 minutes to download the entire game.
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Additional comment
The attached calculator screen shows conversion to hours and minutes. Hours, minutes, seconds are computed "base-60" the same way that Degrees, minutes, seconds are computed "base-60". 250 minutes is converted to hours by dividing by 60 min/hour. We can use the →DMS function of the calculator to show decimal or fractional hours in hours : minutes : seconds. In this use of that function, degrees represents hours.
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