Or you could look at it like this:
You have 1 eighth,
Multiply this by 2 and what do you get? 2 eighths, or 2/8, which can be simplified down to 1/4, which equals 0.25.
$${\mathtt{2}}{\mathtt{\,\times\,}}\left({\frac{{\mathtt{1}}}{{\mathtt{8}}}}\right) = {\frac{{\mathtt{1}}}{{\mathtt{4}}}} = {\mathtt{0.25}}$$
.Or you could look at it like this:
You have 1 eighth,
Multiply this by 2 and what do you get? 2 eighths, or 2/8, which can be simplified down to 1/4, which equals 0.25.