Using Variables (Letters Stand for Numbers) Resource Bundle for 6th Grade Math Centers: These 10 paper and digital resources are aligned with Common Core Standard 6.EE.2: Write, Read, and Evaluate Numerical Expressions in which Letters stand for Numbers. These Exit Slips, Task cards, Worksheets, Quizzes, and Interactive Notebooks are great for whole-class games, math centers/stations, fast finishers, extra practice, homework, scavenger hunts, quiz-quiz-trade, morning work, small groups, or revie