Hello, GAdams!

When you cut a piece of A4 paper in half (portrait, cut across)

you get two pieces of A5 paper.

A5 paper is similar to A4 paper.

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

Another approach (to me, the obvious one) . . . make a sketch! Code:

- *-----------* -
: | | :
: | | ½L
: | | :
L * - - - - - * -
: | | :
: | | ½L
: | | :
- *-----------* -
: W :

A4 has length , width .

A5 has length , width .

We want the ratio: .

Since the rectangles are similar: .

Hence: .

Therefore: is about **70.7%** of .