A transparent square sheet shown above is folded along the dotted line (a diagonal). The folded sheet will look like ________________.
A. A square with a triangular flap on the top-right, fold crease running bottom-left to top-right
B. A triangle with a smaller triangle overlapping inside, forming a symmetric diamond outline
C. A right-angled triangle showing two layers aligned perfectly (the transparent sheet folds one half exactly over the other)
D. A square with a triangle cut-out in the lower-left corner
GATE 2021 · General Aptitude · Paper Folding · medium
Answer: C — the folded sheet looks like a right-angled isosceles triangle (the two halves overlap perfectly).
Identify the fold line: The dotted line on the square runs from one corner to the diagonally opposite corner. This is the main diagonal. Folding along it splits the square into two congruent right-angled isosceles triangles.
Perform the fold: Lift one triangular half and place it exactly over the other. Because both halves are congruent, all edges and corners align perfectly. The result is a right-angled isosceles triangle of half the original area.
Match with options: Option C shows a right-angled triangle with both layers coinciding and no displaced or misaligned edges. This matches the folded result. Options A, B, D show shapes inconsistent with a clean diagonal fold of a square.