Geometry
posted by Anonymous .
Zoe the goat is tied by a rope to one corner of a 15 meterby25 meter rectangular barn in the middle of a large grassy field. Over what area of the field can Zoe graze if the rope is 10 meters long? 20 meters long? 30 meters long?

a 10m rope allows grazing over 3/4 of a 10m circle
3/4 * π * 100 = 75π
a 20m rope allows grazing over 3/4 of a 20m circle + 1/4 of a 5m circle
3/4 * π * 400 + 1/4 * π * 25 = 306.25 π
a 30m rope allows
3/4 of a 30m circle
+ 1/4 of a 15m circle
+ 1/4 of a 5m circle 
Where did you get the 5?