Two identical rectangular crates are packed with cylindrical pipes, using different methods. Each pipe has diameter 10 cm. A side view of the first four rows of each of the two different methods of packing is shown below.
After the crates have been packed with 200 pipes each, what is the positive difference in the total heights (in cm) of the two packings?
Crate A: $20$ pipes high ($200/10=20$)
Crate B: $10$ pipes then $9$ on top, for $19$ in these two rows. Then $19$ goes into $200$ ten times. After $10$ of these $10,9$ groups, then we will have another $10$ row on top. This is $10(2)+1=21$ pipes high.
The difference is $1$ pipe.