When you cut a piece of A4 paper in half (portraiot way up, cut across) youget two pieces of A5 paper.

Ignoring its thickness, A5 paper is similar to A4 paper.

Express the length of A5 paper as a percentage of the length of A4 paper.

OK, I get that A5 is 1/2 of A4. So, that would make it 50% of A4. But this is wrong.

Could someone please explain this step by step please?