SOLUTION: Karen is twice as old as Lori. Three years from now, the sum of their ages will be 42. How old is Karen?

Since "Three years from now, the sum of their ages will be 42",  the sum of their ages now is 42-2*3 = 36 years.


Thus Karen is twice as old as Lori, and the sum of their ages is 36 years.


Hence,  Karen is 24 years old, while Lori is 12.