This Fluency Activity is a part of the Lesson 12, Unit 4, Grade 1. This fluency activity strengthens students' understanding of the relationship between addition and subtraction while providing practice with adding and subtracting multiples of 10. Write two related addition and subtraction sentences using 0-4 tens in unit form. Students convert the number sentences to numeral form and solve (e.g., 40 - 30 = 10 and 30 + 10 = 40).