You have to divide
[tex]2\div\frac{1}{4}[/tex]When you divide by fractions, you have to invert the fraction on the denominator place.
[tex]\frac{1}{4}\rightarrow\frac{4}{1}=4[/tex]This inverted fraction is called a reciprocal fraction.
Once you've obtained the reciprocal fraction you have to multiply it by the numerator of the fraction:
[tex]2\div\frac{1}{4}=\text{ 2}\cdot4=8[/tex]