On Sun, 13 Apr 2008 11:41:56 -0700 (PDT),
<dzogchener@[EMAIL PROTECTED]
> wrote in
<news:bfc67021-aa78-473a-ba08-44aabd8b7212@[EMAIL PROTECTED]
>
in alt.math.undergrad:
> On Apr 13, 5:25 pm, "Brian M. Scott" <b.sc...@[EMAIL PROTECTED]
> wrote:
>> On Sun, 13 Apr 2008 08:03:41 -0700 (PDT),
>> <dzogche...@[EMAIL PROTECTED]
> wrote in
>>
<news:de9d8f03-80df-432e-9a5f-04eb2a979a24@[EMAIL PROTECTED]
>
>> in alt.math.undergrad:
>>> I have been swatting up using a book I purchased, which
>>> has a question about area:
I didn't notice this before, but it's the source of your
trouble: this is *not* a problem about area. See below.
>>> How much will it cost to build a wall round a house that
>>> is 25 metres long and 75 metres wide, if the cost of 50
>>> cm is £10? Your options are A) £4,000, B) 40,000 or C)
>>> £400. The answers are meant to be estimations,
>>> What is the answer? I have calculated the answer, but when I checked
>>> it I found I was wrong, but I cannot get the supposed answer. I am
>>> trying to just work out if the book is wrong or not.
>> The wall is to be 25 + 75 + 25 + 75 = 200 metres long. Each
>> half-metre costs £10, and the wall is 400 half-metres long,
>> so ... .
> OK, I didnt do that. I took 25 * 75 which gives you 1875 m.
No, it gives an *area* of 1875 *square* metres within the
fence/
[...]
> I thought this was an area question, hence 25 * 75....so I
> need to think about what you did with just the additions,
The fence has two short sides of 25 m. each and two long
sides of 75 m. each; I just added up the lengths of these
four sides.
> I obviously dont understand the question!
You need to keep your units straight. The price is quoted
in pounds per unit of length, not pounds per unit of area,
so to get a total price, you clearly need to find a length
-- the length of fencing required. When you multiply two
lengths in metres, however, you get an area.
Brian
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