Folded A4

What shapes can be made by folding an A4 sheet of paper only once?
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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) 

Image
Folded A4
                              b) 
Image
Folded A4


c) 
Image
Folded A4
                                    d) 
Image
Folded A4


e) 
Image
Folded A4

 



If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.