Astudent is downloading his digital textbook. after 17 minutes, he's dismayed to find that there's still 81% of the download left. how long, to the nearest minute, is the total download?

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It is already given in the qustion that after 17 minutes there is still 81% of the download reamining. This means that in 17 minutes the total download that took place is only 19%.
Based on this knowledge, the answer to the question can definitely be deduced.
So
The time taken for downloading 19 percent of the digital textbook = 17 minutes
Then
The time taken by the student for
 downloading 100 percent of the digital text book = (17/19) * 100 minutes
                                                                               = 1700/19 minutes
                                                                              = 89.47 minutes
So at this rate the student will need 89.47 minutes to complete the downloading of the digital text book.

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