Which one does not belong with the other three? explain your reasoning. 40% , 2/5 , 0.4 , 0.04

First change them all to the same form so it's easier to figure out 

40% = 0.4
2/5 = 0.4
0.4 = 0.4
0.04 = 0.04

now you can see which one doesn't belong with the other three as three of them are 0.4 or 0.40 (its the same thing) but the fourth one is 0.04

0.4 is like 40 cents 
0.04 is like 4 cents 

hope you understand this!