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GATE CSE 2021 Set 2 Q2: Transparent square sheet folded along a dotted line

Question

A transparent square sheet shown above is folded along the dotted line. The folded sheet will look like ________.

The sheet (top) and the four options (A)–(D) are shown in the figure.

Top: a square sheet with a vertical dotted line in the middle; a curve rises from the left edge to a peak on the dotted line and falls to the right edge, with two short vertical ticks on the left part and two short horizontal ticks on the right part. Bottom: four half-width folded sheets labelled (A) to (D), each showing a different arrangement of the two curves and tick marks
Tap the figure to enlarge

Try it: multiple choice: exactly one correct option

Select one option
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Answer: B (official GATE 2021 final answer key)

Concept used: Folding a transparent sheet reflects one half onto the other across the fold line, and both halves stay visible.

First step: Mirror the left half across the dotted line: the rising curve becomes a falling curve starting at the peak, and the vertical ticks become mirrored ticks inside the lens it forms with the right curve.

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Source: official GATE 2021 Set 2 CS question paper and final answer key, organised by IIT Bombay. Question paper · Answer key

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