What numbers can you make with 1, 2, 3, and 4, using the operations of addition, subtraction, and multiplication? Work on these problems builds arithmetic fluency and provides opportunities to identify patterns, develop and defend arguments, and create conjectures. This investigation also highlights how thin the boundary is between a fun warm-up activity for fifth graders and deep questions investigated by research mathematicians!

After studying James Tanton’s MTC session about bicycle tracks, avid bicyclist Michael Nakamaye started questioning the mathematics behind how a bike works.

How do gears work? How many teeth are there usually on the different gears? Why? How is a bike like a ratio machine?