1/2 divided by 1/4 means, 1/2 is broken into equal parts of 1/4. You know that 1/4 * 2 = 1/2, this means there are two equal 1/4 parts in 1/2. Thus, the answer is 2.
Still if you did not understand, see this
|____|____| Consider, this is a box whose length is 1 cm. It is divided into two equal parts of 1/2 cm.
Now I divide one of the part (1/2 cm) by 1/4. i.e I break that part into many smaller parts all equal to the 1/4 cm i.e