The figure in Panel I below is a grid of cells with four rows and four columns. The numbers on the top and on the left represent the number of cells that are to be shaded in that column and row, respectively. Which one of the options shown in Panel II below represents the grid shaded correctly?
Show Hint
Count the shaded cells in each row and each column of every option and compare with Panel I's numbers.
A grid-shading puzzle like this is solved by treating the row numbers and column numbers as two separate checks that a correct panel must pass together.
Option A, panel (i): Counting shaded cells row by row gives 3, 2, 1, 2 from top to bottom. The needed pattern is 3, 1, 2, 2, so the middle two rows are swapped and this panel fails.
Option B, panel (ii): Counting row by row gives 3, 1, 2, 2, which is exactly the target row pattern. Counting column by column, every column also comes to 2, matching the target of 2 in each column. Both checks pass, so this panel is correct.
Option C, panel (iii): The row counts again come out as 3, 2, 1, 2, the same mismatch as panel (i), so it fails.
Option D, panel (iv): The row counts come out as 3, 1, 1, 3, which does not match the needed 3, 1, 2, 2 pattern, so it fails too.
Since panel (ii) is the only one whose rows and columns both match Panel I's numbers, option B is correct.
