Scientific notation into binary notation

Question

$0.25E3 = 0.25 \cdot 10^3 = 250$. I am trying to write it in binary notation which should be something like for example if binary is $11111010$ then the binary would be in scientific notation $0.11111010 \cdot 2^7$. Here I am really confused how much I should place the dot in the left side. what is the actual expression. I understand it would be minus when point goes to right side and positive when goes to left side. But how many times it has to go and on what basis?