2.NOS.B.6: Recall or quickly derive addition and subtraction facts within 20. a. Use counting, make ten, and ten more/less, doubling strategies to add and subtract. b. Use the use ten strategy (e.g., think of 9 + 1 + 6 to solve 9 + 7) and doubles plus one strategy (e.g., think of 4 + 4 + 1 to solve 4 + 5) to add and subtract. c. Use the inverse operation to add and subtract (e.g. think of 7 + ? = 15 to solve 15 – 7 = ?).