Theme 9.  Addition with regrouping within 20

In the theme you learn:
• You will practice how to solve addition and subtraction expressions within 20 without regrouping;
• You will learn how to do addition within 20 with regrouping;
• You will learn to add one-digit numbers with regrouping by splitting numbers into easy addends;
• You will improve your skills to find the unknown addend, unknown subtrahend, and the difference;
• You will solve problems to find the unknown subtrahend, compare numbers by difference, and increase a number by a few units.