<PRE><B>Question 836017</B>
A rectangular lawn measures 60ft. by 80ft. 
 Part of the lawn is torn up to install a sidewalk of uniform width around it.
 The area of the new lawn is 2400 sq/ft. How wide is the sidewalk?
:
Find the original area: 60 * 80 = 4800 sq/ft
Find the area of the walkway: 4800 - 2400 = 2400
:
let x = the width of the walk
;
(60-2x)*(80-2x) = 2400
FOIL
4800 - 120x - 160x + 4s^2 = 2400
Arrange as a quadratic equation
4x^2 - 280x + 4800 - 2400 = 0
4x^2 - 280x + 2400 = 0
simplify, divide by 4
x^2 - 70x + 600 = 0
Factors to
(x-10)(x-60) = 0
x = 10 ft, the only one that makes sense</PRE>