This may help people:

> Mary is 24 years old. She is twice as old as Ann was (12) when Mary was as old (18) as Ann is now (18). How old is Ann?

So 6 years ago, Mary was 18, and Ann was 12.

Today, Mary is twice the age that Ann was (12 * 2) at the time that she (Mary) was 18, making her 24.

What makes it confusing is that the sentence is comparing Mary’s present age with Ann’s past age (which I did not catch until mulling it over a bit).

Yeah, I had to spell it out to get it to click for me

> mary is 24

> 8 years apart: ann is 16 now, when ann was 12 mary was 20

> 6 years apart: ann is 18 now, when ann was 12 mary was 18

> 4 years apart: ann is 20 now, when ann was 12 mary was 16