Answer:
8 inches
Explanation:
You want the diameter of a circle that has a circumference between 20 and 27 inches, expressed as an integer number of inches near the high end without going over.
Diameter
The relationship between diameter and circumference of a circle is ...
C = πd
d = C/π
For the given circumference range, the diameter range is ...
20 ≤ πd ≤ 27
20/π ≤ d ≤ 27/π
6.4 ≤ d ≤ 8.5
Integers in this range are 7 and 8. The largest one is 8.
8 inches is the most reasonable diameter of the circular cardboard model.