GATE 2023 BT – Question 5
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)
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Correct answer: (C) 5
Explanation
Reflect each initially black square across both axes. Their symmetry orbits occupy eight squares in total, requiring five additional black squares.