Sorry to go on about this (because this is the second thread on the same subject) but to say the correct form is 'bet' is not entirely true. If you look up the word 'bet' in www.onelook.com that everyone here keeps recommending, of the first 13 results 1,2,3,5,6,10,11,12 and 13 all list 'betted' as one of the forms of the verb. 4,7 and 9 are not dictionaries. Only 9, the Cambridge Advanced Learner's Dictionary doesn't. I know it's not common, but it exists.
If you have a question about the English language and would like to ask one of our many English teachers and language experts, please click the button below to let us know: