Ratio Language
First you need to know what this means... example "For every vote candidate A received, candidate B gets five votes." this would be shown as 1:5
The example here in the problem is 5 minutes for 500 yards as 5:500
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For your example the 20 minutes and 7 pages, 20:7 pages your unit rate would be 2.85714286 minutes you read one page, or rounded to the tenths 2.86 minutes you read a page