If I give my brother 2 marbles I will have double his number of marbles, but my friend will have triple the number I do. The total number of marbles we have together is 63. How many marbles do I have? Let's be accurate as possible.
Let X be the number of marbles I have. If I give my brother 2 marbles, I'll have X - 2 marbles left. And my brother will have (X - 2) / 2 marbles. And my friend will have (X - 2) * 3 left. So the total number of marbles is X - 2 + (X - 2) / 2 + (X - 2) * 3 = 63. (X - 2) * 9 / 2 = 63. X - 2 = 14. X = 16 marbles.
The answer: 16.