The number of pages the student can read in a minute is an illustration of rates.
The time left to complete the whole book is 90 minutes
From the complete question, the student's rate is:
The number of pages is:
First, we calculate the time to read the whole book
The number of the student has read is:
Next, we calculate the time spent on the 25 pages
Convert to minutes
So, the time left is:
This gives
Convert to minutes
Hence, the time left is 90 minutes
Read more about rates at: