Marbles & Stamps: How Many Did Casey Buy?

[wailingkoh]

I have a question

Carey bought some marbles and gave half of them to Casey. Casey bought some stamps and gave half of them to Carey. Carey used 5 stamps and Casey gave away 11 marbles. The ratio of the number of stamps to the number of marbles Carey had left then became 1 : 7 and the ratio of the number of stamps to the number of marbles Casey had left became 1 : 5. How many stamps did Casey buy?

 

[phymat]

So what is the problem? Have you tried anything? Post your attempt (or at least something which explains your difficulty in solving the question).