What is the number between 0.4 and 0.5?

There are infinite numbers between 0.4 and 0.5. The reason is that there are infinite rational as well as irrational numbers between 0.4 and 0.5, therefore, we cannot exactly give all the numbers between 0.4 and 0.5. 

These are the numbers

0.41,0.42,0.43.0.44,0.45,0.46,0.47,0.48,0.49

X=y+4 is the answe