689
3 and 37
51 + 29 = 80
They are: 29+5 = 34
I'd say it's 48. To fit the pattern, it should be 58. If you take 1 and 2 and add them the answer is 3, you will use that answer several more times you will also add some numbers to them selves such as follows. 1+2=3 3+2=5 5+5=10 10+3=13 13+13=26 26+3=29 29+29=58 Thus making 48 the one that does not belong.
As 29 is a whole number, if you wish to make it a decimal number, all you have to do is add a .0 to the end. This, 29.0 is the decimal form of 29.