I might will try to guess 15 number / character at one transaction , is it possible btw?
According to their FAQ...
3. Can I generate multiple addresses and send bitcoins to them in a single transaction?
No. Only the amount sent to the first address generated will be considered as bet and all other amounts sent in that transaction will be considered as donation.
So, u can not place bets in one Tx to multiple addresses, but can send multiple Tx to multiple addresses.