Folded a4
Problem
A sheet of A4 size paper (297mm x 210mm) is folded once and then laid flat on the table.
Which of these shapes could not be made?
a) 
c) 
e) 
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
Student Solutions
Answer: b
The diagrams show the fold lines that produce each of the four possible shapes.
The shape formed by folding along a line between two opposite corners is shown in blue.
a) 
c) 
e) 