SOLUTION: I don't have a clue how to work this one out. I worked it out but it was wrong on the quiz. A concrete driveway has a perimeter of 280 feet. The length of the driveway is 20

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: I don't have a clue how to work this one out. I worked it out but it was wrong on the quiz. A concrete driveway has a perimeter of 280 feet. The length of the driveway is 20      Log On


   



Question 264741: I don't have a clue how to work this one out. I worked it out but it was wrong on the quiz.

A concrete driveway has a perimeter of 280 feet. The length of the driveway is 20 feet more than 4 times its width. Find the length and width of the driveway by writing two equations with two varibles, and solving the equations by either the addition method or the substitution method.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = the length in feet
Let b = the width in feet
Let p = perimeter in feet
The formula for perimeter is:
p+=+2a+%2B+2b
I'm given that p+=+280 ft
(1)280+=+2a+%2B+2b
Also given is:
(2)a+=+4b+%2B+20 ft
---------------------
Divide both sides of (1) by 2, and
swap left and right
(1) a+%2B+b+=+140
Subtract 4b from both sides of (2)
(2) a+-+4b+=+20
Now subtract (2) from (1)
(1) a+%2B+b+=+140
(2) -a+%2B+4b+=+-20
5b+=+120
b+=+24
And, since
a+%2B+b+=+140
a+%2B+24+=+140
a+=+116
The length is 116 ft and the width is 24 ft