Question: This is an IQ question.

"Catherine is now twice as old as Jason but 6 years ago she was 5 times as old as he was. How old is Catherine now?"

How to solve such questions? I think their combined age should be given but its not.

Answer: 
First you have to formulate the given information in maths. We write $C$ and $J$ for the ages. Since Catherine is twice as old as Jason we have
$$C = 2J.$$
Moreover we know that 6 years ago, Catherine was five times older then Jason. This can be formulated as
$$ C - 6 = 5 \cdot (J - 6) = 5J - 30.$$
This equation is equivalent to
$$C = 5J - 24.$$
Subtracting the equations yields
$$0 = 3J - 24$$
and thus $J = 8$ and $C = 16$.
**hint**: Let $C,J$ be Kathy's and Jason's ages as of now. Thus: $C = 2J , C-6 = 5(J-6)$. Can you finish it off?