Question

a building in a city has a rectangler base. the length of the base measures 60 ft less than three times the width. the perimeter of this base is 880. what are the dimensions of the base? @DebbieG

Answer 1

You had almost the identical problem here:
http://openstudy.com/users/anton99#/updates/52310eb7e4b03eb771a2610b
and it was pretty much done for you. Did you try to work through that one and understand it?

And have you tried to sketch this one?

Answer 2

yeah i tried except its 3 times

Answer 3

i keep getting the wrong answer

Answer 4

" the length of the base measures 60 ft less than three times the width."

How can you put that into a mathematical expression? use W for width.

Then L=??? (in terms of W)

Answer 5

yeah how can u

Answer 6

If W is width, then what is "3 times the width"?

Answer 7

3w

Answer 8

Good. Now, what is:

"60 ft less than three times the width."

Answer 9

3w-60

Answer 10

See? You understand more than you think you do, you just need to think it through one step at a time! :)

Now you have:

L=3W - 60

That "models" the information in the problem: " the length of the base measures 60 ft less than three times the width."

Now we will do something with that, by using the perimeter information:

Answer 11

You are told that perimeter is 880.

and there is a STANDARD formula for perimeter of a rectangle (you should know this!)

P=2L + 2W

Now, you have L=3W - 60, and what THAT does is allow us to take the perimeter equation (which has TWO unknowns, L and W), and make a substitution so that we end up with an equation with just ONE variable - and that, we can solve.

Answer 12

So we have to SUBSTITUTE the expression for length, L=3W - 60, into the perimeter equation - just "drop it in" where we have the L! And also, put in the "known value" of perimeter, for P:

P=2L + 2W
880=2(3W - 60) + 2W

Answer 13

Are you with me? Stop me if you don't understand something to this point.

Answer 14

ask questions.

Answer 15

125 = w

Answer 16

Exellent!! That's correct!

And now, all you need is to get length... guess what? you have a conveeeenient formula for length, in terms of W:

L=3W - 60

So just take that W that you just figured out, and plug & chug in the length formula, and tah-dah, you have length and width. :)

Answer 17

275?

Answer 18

For length? Not quite.....

Answer 19

L=3W - 60

plug in W=125....

Answer 20

GOT IT