Question 1208468
<pre>
It might help students more if instead of lambasting problem creators or the
students for miscopying problem or for not understanding what we think they
ought to understand, that we make up sensible problems similar as possible to
what they posted.  So I decided to do that instead.

I won't mix grams and kilograms, since it would be unusual and awkward to
measure weights of candy bars in kilograms. Also I'll change the 9% to 20% so
the answer will come out prettier. Here goes:</pre>A candy manufacturer decided to decrease the weight of each candy bar 
by 20% while retaining the price. What was the resulting percent increase 
in the price per gram.<pre>Suppose previously, a candy bar had sold for price p cents and weighed w grams.
 
Therefore the OLD price per gram was
 
{{{matrix(1,2,p,cents)/matrix(1,2,w,grams)}}} or {{{matrix(1,2,p/w,cents/gram)}}}

Now the weight has been changed from w grams to 100%-20%=80% of w grams or 0.80w
grams.

Therefore the NEW price per gram is

 {{{matrix(1,2,p,cents)/matrix(1,2,0.80w,grams)}}} or  {{{matrix(1,2,p/0.80,cents/gram)}}}

Now we first compare the NEW price per gram to the OLD price per gram by
dividing the NEW by the OLD:

{{{(p/(0.80w))/(p/w))}}}

Invert and multiply:

{{{(p/(0.80w))*(w/p)}}}

{{{(cross(p)/(0.80cross(w)))*(cross(w)/cross(p))}}}

{{{1/(0.80)}}}{{{""=""}}}{{{1.25}}}{{{""=""}}}{{{"125%"}}}

Since the NEW price is 125% of the OLD price, it means the
new price has been increased 25% (over 100% of the OLD price).

So even though we cannot know the OLD or NEW price or the OLD
or NEW price per gram, we still know that the OLD price per 
gram, whatever it was, was increased by 25%.

Edwin</pre>