Question 696182
mary is 24 years old. mary is twice as old as ana was when mary was as old as ana is now. how old is ana?
<pre>The other person's answer, 18-years-old is correct!
Age-related problems like this can be a real HEADACHE, but once you  get used to them, they become a "breeze" to figure out. 

One KEY piece of information that needs to be derived is who's OLDER. The statement, "when mary was as old as ana is now" 
clearly shows that Mary is older.

With Mary being the older person, and with Ana's age being A, the difference in their ages is: M - A, or 24 - A, since Mary is 24.
Mary was Ana's age, "24 - A" years ago, at which time Ana was A - (24 - A), or 2A - 24
Now, since it's stated that, "mary is twice as old as ana was when mary was as old as ana is now," we get 
the following equation: 24 = 2(2A - 24)
                        24 = 4A - 48
                   24 + 48 = 4A
                        72 = 4A
Ana, or {{{highlight_green(matrix(1,6, A, "is:", 72/4, "=", 18, years-old))}}}</pre>