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GATE 2023 PH – Question 5

General Aptitude · Spatial Aptitude: Spatial Reasoning and Visualization · 1 mark · Multiple choice

A line of symmetry is defined as a line that divides a figure into two parts in a way such that each part is a mirror image of the other part about that line. The given figure consists of 16 unit squares arranged as shown. In addition to the three black squares, what is the minimum number of squares that must be coloured black, such that both PQ and MN form lines of symmetry? (The figure is representative)

Sixteen squares and two proposed reflection axes.
  1. 3
  2. 4
  3. 5
  4. 6 M N P Q

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Correct answer: (C) 5

Explanation

Reflect the three marked cells in both axes and take the union of the resulting symmetry orbits. Eight cells are required, so five more must be filled.