The symbols ○, ✱, △, and □ are to be filled, one in each box, as shown below.
The rules for filling in the four symbols are as follows.
1) Every row and every column must contain each of the four symbols.
2) Every 2×2 square delineated by bold lines must contain each of the four symbols.
Which symbol will occupy the box marked with '?' in the partially filled figure?
[The figure is a 4 × 4 grid; bold lines divide it into four 2×2 squares, rows 1-2 and 3-4 by columns 1-2 and 3-4. Empty boxes are left blank.]
| ? | △ | ||
| ○ | ✱ | ||
| □ | ✱ | ||
| ✱ | △ | ○ |
GATE ME - 2023,
Answer: B
The box takes ✱ (the star).
Number the rows and columns 1 to 4 from the top left; '?' is in row 1, column 2.
- In the top-right 2×2 square, row 2, column 4 cannot be ○ (row 2 already has ○) and cannot be △ or ✱ (both are already in that square), so it is □.
- That leaves ○ for row 1, column 3, the last empty box of the top-right square.
- Row 1 now has ○ and △, so its two empty boxes take ✱ and □. Column 1 already has ✱ in row 4, so row 1, column 1 is □ and '?' is ✱.
○ and △ are already in row 1, so they cannot repeat there, and □ is forced into column 1, leaving the star as the only symbol for the marked box.
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