Question 23
Sebastien has a square paper serviette of side 24 cm. He folds it along a diagonal to form triangle $ABC$, right-angled at $A$. He then folds $C$ onto a point $D$ on $AB$; this fold meets $BC$ at $X$. He next folds $B$ onto $X$, and this new fold passes through $D$. What is the distance $AD$, in centimetres?