Shaded and unshaded squares are arranged in rows so that:
the first row consists of one unshaded square,
each row begins with an unshaded square,
the squares in each row alternate between unshaded and shaded, and
each row after the first has two more squares than the previous row.
The first 4 rows are shown.
The number of shaded squares in the 2020th row is
The 1st row has 0 shaded squares and 1 unshaded square.
The 2nd row has 1 shaded square and 2 unshaded squares.
The 3rd row has 2 shaded squares and 3 unshaded squares.
The 4th row has 3 shaded squares and 4 unshaded squares.
Because each row has 2 more squares than the previous row and the squares in each row alternate betweeen unshaded and shaded, then each row has exactly 1 more shaded square than the previous row.
This means that, moving from the 4th row to the 2020th row, a total of additional shaded squares are added. Thus, the 2020th row has shaded squares.