If l=2w-10 and 2l+2w=400 what is l

Question

Finding length of parking lot. Length is ten meters less than two times the width and the lot has a perimeter of 400 meters. Solving for length

Answer 1

You may substitute the value for l (2w-10) into the second equation (2l+2w=400) to solve for w, then put that value of w into either equation to solve for l,

-- OR --

You can solve for l directly by eliminating w:

      L  - 2W  = -10    [from first equation]

    2L + 2W  = 400     [second equation]

  --------------------------    [elimination; add equations]

    3L           = 390

     L         = 130

Answer 2

2l + 2w = 400

2(2w-10) + 2w = 400

4w - 20 + 2w = 400

6w - 20 = 400

6w = 420

w = 70 meters

l - 2w-10 = 2(70) - 10

l = 130 meters