Answer:
3 3/4 feet
Explanation:
Given
Perimeter of the garden = 20ft
If he wants the length of the garden to be 2 1/2 longer than its width, then;
L = 2 1/2 + W
L is the length
W is the width
Perimeter of the garden = 2(L+W)
P20 = 2(5/2 + W+W)
20 = 5 + 2W+2W
20 - 5 = 4W
15 = 4W
W = 15/4
W = 3 3/4 ft
Hence the width of the garden is 3 3/4 feet