There is nothing like doubling your coins, if you want to double then you need to put efforts and work hard to achieve it there is no short cut to success.
Yup! there is no such thing as easy in doubling your coins especially when it is bitcoin, you will totally need to work hard, time, knowledge, skill and patient to do this and to do successful trading you will also need all of this in achieving your double coins.
Yes without making efforts you cannot double your coins, many sites promises to double your coins but those all are ponzi so beware of those scammers.
Yup! there are surely a lot of ponzi sites out there that is why you will need to try and study their sites first before letting them have your money because it will be a trouble if they would end up scamming your bitcoins and then you will feel sorry for what you did!