Question

Jack buys a bag of 5 apples each equal in size he eat 1/2 of one Apple what fraction did he eat

Answer 1

You have $4\frac{1}{2}$ apples left. 
You have 5 whole apples, you took one whole apple out, which equals 4 whole apples left. Then with the whole apple you took out, you ate $\frac{1}{2}$ of it.
 Jack ate $\frac{1}{2}$ of an apple in 5 apples. 
If you say that Jack ate $\frac{1}{2}$ of 3 apples, then he ate $1\frac{1}{2}$ apples. So there isn't any difference when he ate $\frac{1}{2}$ of an apple.