Ruth can read 15 pages in 30 minutes. She decides to create a table to keep track of her progress. From the data provided, at what ratio is the unit rate (constant of proportionality) represented?

Times (hours). Pages read
1/2. 15
1. 30
1 1/2. 45
2. 60

The ratio of pages read to time in hours is constant at 1:2. For every 1 hour, Ruth reads 30 pages.