The area of a 300' by 400' rectangle is doubled by adding a strip of width around the perimeter. Approximately how wide is that strip?

Answer 1

old area = 300*400 = 120 000
new area = 240 000

(300+2x)(400+2x) = 240000
120000+1400x + 4x^2 = 240000
simplify and divide by 4.

x^2 + 350x - 30000 = 0
x = (-350 ± √242500)/2
= appr 71.22 or some negative which we will reject