This Fluency Activity is a part of the Lesson 10, Unit 4, Grade 2. This fluency exercise reviews the mental math strategy taught in Lesson 4, which was to use compensation by breaking apart one addend to make the other addend into a multiple of 10 and, therefore, easier to add mentally. To use compensation with subtraction, add the same number to the minuend and subtrahend to make a multiple of 10.