Question 181920
 The eighth hole at a golf course has a circular green with a radius of 20 yards. There is a moat of uniform width surrounding the green. The area of the moat and green is four times the area of the green. How wide is the moat? Please give answer in 3 decimal places.
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Find the area of the green. Its radius is given, so that's easy.
Then, the total area is 4 times that.  Find the radius from the total area.
Then, subtract 20 yards from it to get the width of the moat.