Since Speed! is a skip-counting game and Cuisenaire Rods are a math manipulative, they go great together.
The blue Cuisenaire Rods are 9 cm long and the white rods are 1 cm long.
When the 4 cm purple rods and the 5 cm yellow rods were combined into 9 cm rods, the number of square units was more difficult to determine.
9 x 9 = 81 = 9 x 4 + 9 x 5 = 36 + 45
The Nine Speed deck was used to look up the 81, the Four Speed deck was used to look up the 36 and the Five Speed deck was used to look up the 45. After my daughter added 36 and 45 she was excited to learn the unit area could be determined two different ways.
* I did not receive any compensation for this recommendation (Cuisenaire Rods). I'm just a homeschooling mom who has found many products that I like. If you're interested in the products I recommend on this blog I want to make it easy for you to find them.
** I am an Amazon associate and receive a small portion of the sales on orders made after clicking in from this site, which I promptly spend on homeschooling books and supplies for my children.
*** Highhill Educational Supplies is my company. I am the creator of the game Speed!