Answer:
1/4 divided by 1/2 equals 1/2
Real-world problem:
A constructor official knows that he needs 1/2 sack of cement to produce 10 blocks of concrete for a wall. The official only has 1/4 of the sack left and want to know how many blocks he can produce with this material.
Explanation:
Since you know that 1/2 of the sack is needed to make 10 blocks, you can use this information to find the number of blocks that 1/4 of a sack can make. The question you want to answer is:
if
of a sack produces 10 blocks, how may blocks
of a sack can produce?
Using the Rule of Three you can solve

Now you know that 1/4 of a sack can produce 1/2 the number of blocks that 1/2 of the sack can produces, this means that you can produce 5 blocks of concrete.