N is the number of shopping carts in the train.
length_cm is the total length of the train in centimeters.
notes is where we recorded a few unusual circumstances.
How long is one shopping cart?
How much does one shopping cart fit into the next one?
Do any of the notes seem to make a difference?
One set of carts was 486 cm long. How many carts?
(data by Susan English and Tim Erickson, 2004)