A rectangular garden is 80 m by 60 m. Part of the garden is torn up to install a strip of lawn of equal width around the garden. The new area of the garden is 800 m squared. How wide is the strip of lawn?

Step-by-step explanation:

let x < 30 be the width of strip of lawn.

then (80-2x) (60-2x) = 800

4800-160x-120x+4x²=800

4x²-280x+4000=0

x²-70 x+1000=0

x²-20x-50x+1000=0

x (x-20) - 50 (x-20) = 0

(x-20) (x-50) = 0

x=20,50

x=50 (rejected)

x=20 m