Current location - Training Enrollment Network - Mathematics courses - Mathematical problems. Excuse me, what do you mean by that method? I don't understand.
Mathematical problems. Excuse me, what do you mean by that method? I don't understand.
In line 1, the number in the second column is: 1×2=2.

The number in the third column of row 2 is: 2×3=6.

The number in the fourth column of the third row is 3×4= 12.

.........................................

The number in row m and column (m+ 1) is m×(m+ 1).

Therefore, the number of rows of 20 and 2 1 is 20×2 1=420.