Question 661745
<pre>
Mary is 24 years old.  
Let Ann be A years old. 

Mary is twice as old as Ann was x years ago, which was (A - x). 
Also x years ago, Mary was (24 - x), and that is how old Ann is now,
which is A. 

x years ago, Mary was 24 - x
x years ago, Ann was A - x

So the equations comes from:

         {{{(matrix(3,1,

"Mary's", age, now))}}} = 2·{{{(matrix(5,1,

"Ann's", age, x, years, ago))}}}

and

         {{{(matrix(5,1,

"Mary's", age, x,years, ago))}}} = {{{(matrix(3,1,

"Ann's", age, now))}}}

So the system of equations is

                24 = 2(A - x)
                24 - x = A

Solve that system and get x = 6 and A = 18.

So 6 years ago Ann was 12 and Mary is twice that now.

Edwin</pre>