## CROSS NUMBER PUZZLES—ADDITION AND SUBTRACTION

Students solve a collection of puzzles in which they add, subtract, and use logical reasoning to find missing numbers in a 3 × 3 grid. Through multiple plays of random challenges generated by Sketchpad, students work to improve their strategies and scores. The activity concludes with students identifying the strategies they used to solve the puzzles.

OBJECTIVES
• Students will use puzzles to practice addition and subtraction facts.
• Students will compose and decompose two-digit numbers into tens and units.
• Students will develop strategies, using logical thinking and their understanding of place value, to recognize which rows or columns of a cross-number puzzle are suitable for immediate solution and which require other rows or columns to be solved first.
COMMON CORE CONNECTIONS
Mathematical Practices

(1) Make sense of problems and persevere in solving them; (2) Reason abstractly and quantitatively; (3) Construct viable arguments and critique the reasoning of others; (5) Use appropriate tools strategically; (6) Attend to precision; (7) Look for and make use of structure; (8) Look for and express regularity in repeated reasoning.

Content Standards

1.OA1, 3, 4, 6, 7, 8; 1.NBT1, 2, 4, 6; 2.OA1, 2; 2.NBT1, 5, 6, 7, 9; 3.A1; 3.NBT2