Answer:
3 +9 does not belong because it doesn't equal 10 like the rest of them do.
Well, if any number is higher than '5' it turns one number more. So, here's a good rhyme to help you: "Five or more, up the score, Four or less, let it rest." The maximum number it could be would have to be '444' because it is not bigger than 445, which would turn to 500.
1.4+2.7=4.1 is true the others are false