W.1 Complete addition sentences - sums up to 20

An addition sentence is a number sentence that shows two or more numbers (called addends) being combined into a total (called the sum). It uses the plus sign (+) and the equals sign (=) to show the relationship.

Every addition sentence has specific parts with special names. Knowing these names helps you understand what you are working with.

Addends: These are the numbers that are being added together. In an addition sentence, they come before the equals sign and on either side of the plus sign.

Sum: This is the total amount you get when you combine the addends. The sum always comes after the equals sign.

To complete an addition sentence means to find the missing number that makes the sentence true. The missing number could be one of the addends, or it could be the sum. Your job is to figure out what number is needed to make both sides of the equals sign have the same value.

When one addend is missing, you can use several thinking strategies to find it. These strategies help you solve the problem without just guessing.

Strategy 1: Count On. If the sentence is 4 + ? = 10, start at 4 and count how many numbers you need to say to reach 10. (Say: "5, 6, 7, 8, 9, 10." That's 6 counts.) So, 4 + 6 = 10.

Strategy 2: Use a Related Fact (Think Subtraction). If you know that 10 is the sum and 4 is one addend, you can think: "What number plus 4 equals 10?" This is the same as asking, "10 minus 4 equals what?" So, 10 - 4 = 6.

Strategy 3: Use Known Facts. Remember facts you already know. If you know that 8 + 5 = 13, then you also know that 13 - 8 = 5. This helps you find a missing addend quickly.

When the sum is missing, you are performing the basic act of addition: combining two numbers. For sums up to 20, first graders use powerful mental math strategies.

Strategy 1: Make a Ten. This is a key first-grade strategy. Take one addend and break apart the other addend to make a ten first, then add the rest. For example, for 8 + 6: Take 2 from the 6 to make 8 into 10. You have 4 left from the 6. Then, 10 + 4 = 14. So, 8 + 6 = 14.

Strategy 2: Doubles and Near Doubles. If the addends are the same or very close, use doubles facts. You know 6 + 6 = 12 (a double). So, for 6 + 7, it's just one more: 12 + 1 = 13. For 6 + 5, it's one less: 12 - 1 = 11.

Strategy 3: Count All or Count On. For smaller numbers, you can count all objects (like fingers or drawings). For larger numbers, start with the larger addend and count on the amount of the smaller addend. For 12 + 3: Start at 12, then count "13, 14, 15."

The equals sign (=) does not mean "the answer is coming." It means "is the same as" or "balances." The value on the left side of the equals sign must be exactly the same as the value on the right side.

When completing a sentence like ? + 4 = 11, you are looking for the number that, when added to 4, balances or equals 11.

Fluency means being able to find sums and missing parts quickly and accurately. To become fluent with addition sentences up to 20, you should practice groups of facts systematically.

Group 1: +0 and +1 Facts: Any number plus 0 is that number (9 + 0 = 9). Any number plus 1 is the next number (9 + 1 = 10).

Group 2: Doubles Facts: Memorize doubles: 1+1=2, 2+2=4, up to 10+10=20. These are the backbone for near doubles.

Group 3: Make Ten Facts: The pairs that make 10: 1+9, 2+8, 3+7, 4+6, 5+5. These are essential for the "Make a Ten" strategy with larger sums.

Group 4: Using Ten Frames: Visualizing numbers on a ten frame (a grid of 10 boxes) can help you see how to make ten and what is left over.

After you complete an addition sentence, it is important to check your answer to make sure it is correct. This builds good math habits.

Method 1: Use the Inverse Operation. If you found a missing addend by subtracting, add the two addends back together to see if they equal the sum. If you found a missing sum, subtract one addend from the sum to see if you get the other addend.

Method 2: Use a Different Strategy. Solve the problem a second way. If you used "Make a Ten," check it by "Counting On." If both methods give you the same answer, you are likely correct.

Method 3: Estimate. Ask yourself if your answer makes sense. If the problem is 13 + 4, the sum should be a little more than 13. An answer like 8 would not make sense.