In this lesson, students solve using Rekenrek bracelets and number bonds to show how "partners of 10" lead to related subtraction number sentences. For example, they notice that 10 - 3 = 7 and 10 - 7 = 3 are shown in similar ways with their Rekenrek bracelets (both starting with 10, and involving a group of 3 and a group of 7), and that knowing one subtraction sentence allows them to quickly know the other.