In article <slrnfnq9s8.9o5.dbast0s@[EMAIL PROTECTED]
>, Daniel C. Bastos
<dbast0s@[EMAIL PROTECTED]
> wrote:
> In article <1srgqlrcsg88f$.co8ageth5gmp$.dlg@[EMAIL PROTECTED]
>,
> Brian M. Scott wrote:
>
> > 80% of 15 is 0.8 * 15 = 12, so he got 12 of the 15
> > true-false questions right. [...]
>
> Changing subject: if I were asked why we multiply the percent by the
> amount which we want to find a percent of, I would answer something like
> the following.
>
> By definition, 80% is 80 out of each 100. If we had 15 hundreds, then we
> would have
>
> 80% of 15 hundreds = 80 + 80 + ... + 80 = 80 * 15 = 1200.
>
> If we now divide this equation by 100, we get
>
> 0.8 * 15 = 12.
>
> So we use the x/100 for x% and multiply by the given quantity because it
> is the same thing as augmenting the given quatity in amounts of hundreds
> so that we can extract x out of each hundred and add them as many times
> as necessary to know the total that composes the x% we're interested in.
>
> Thoughts?
80% means 80 things per hundred other things. How many 100's in 480?
Ans: 4.8.
At 80%, how many things are in 480 other things?
80*4.8 = 384. At 25% there are 25*4.8 things. At 10% there are 10*4.8
things.
That is, to do it "properly", divide the number of "other things" by
100 _first_ then multiply by 80. Of course that's not the way it is
usually done. Instead of a*(b/100) we usually do (a/100)*b - I don't
know why.
--
Paul Sperry
Columbia, SC (USA)
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