I have a staircase which looks like this:
Chelsea adds a certain number of rows on the bottom of this staircase and then numbers the squares, like this:
For the previous example we're assuming that Chelsea added 2 rows below the staircase.
The top number in the 15th column is 405. How many rows did Chelsea add below my staircase. I worked out that the 15th column would have the same number of squares as the 15th odd number, which is 29, in a Normal Staircase. However, I don't know how to go about this. Can anyone help me?