Addition Within 20

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Answer Key & Explanations

Addition Within 20 · Grade 1 · Worksheet 2

1. 0 + 8 = ? Answer: 8 Solution: Identify the numbers in the problem. We have 0 and 8. Recognize the operation.
   Full step-by-step solution

   Step 1: Identify the numbers in the problem. We have 0 and 8. Step 2: Recognize the operation. The operation is addition (+). Step 3: Recall the property of zero in addition. Adding zero to any number does not change the number's value. This is called the additive identity property. Step 4: Apply the property. 0 + 8 = 8 Step 5: Write the final answer. The sum is 8.

2. 0 + 15 = ? Answer: 15 Solution: Identify the numbers in the problem. We have 0 and 15. Recognize the operation.
   Full step-by-step solution

   Step-by-step solution: Step 1: Identify the numbers in the problem. We have 0 and 15. Step 2: Recognize the operation. The plus sign (+) tells us we are performing addition. Step 3: Recall the property of zero in addition. Adding zero to any number does not change the value of that number. This is called the additive identity property. Step 4: Perform the calculation. 0 + 15 = 15 Step 5: State the final answer. The sum of 0 and 15 is 15.

3. 3 + 3 = ? Answer: 6 Solution: Identify the numbers to be added. We have the number 3 and the number 3. The plus sign (+) means we are performing addition.
   Full step-by-step solution

   Step 1: Identify the numbers to be added. We have the number 3 and the number 3. Step 2: Understand the operation. The plus sign (+) means we are performing addition. Addition is the process of combining two or more numbers to find their total. Step 3: Perform the addition. Start with the first number, which is 3. Then, count up by the second number, which is also 3. Counting up: 3 ... then 4, 5, 6. So, 3 + 3 = 6. Step 4: State the final answer. Therefore, the total sum is 6.

4. 3 + 2 = ? Answer: 5 Solution: We start with the problem: 3 + 2. The plus sign (+) tells us we need to combine the two numbers together. This is called addition.
   Full step-by-step solution

   Step 1: We start with the problem: 3 + 2. Step 2: The plus sign (+) tells us we need to combine the two numbers together. This is called addition. Step 3: To visualize this, imagine you have 3 apples. Then you get 2 more apples. Step 4: Now, count all the apples you have. Start from the first group: 1, 2, 3. Then continue counting with the second group: 4, 5. Step 5: The total number of apples is 5. Therefore, 3 combined with 2 equals 5. Final Answer: 5

5. Liam has 7 toy cars. His friend Noah gives him 5 more toy cars. How many toy cars does Liam have now? Answer: 12 Solution: Liam starts with 7 toy cars. When Noah gives him 5 more, that means we add 5 to the number of cars Liam already has. Write the addition problem.
   Full step-by-step solution

   Liam starts with 7 toy cars. When Noah gives him 5 more, that means we add 5 to the number of cars Liam already has. Step 1: Write the addition problem. 7 + 5 Step 2: Start from 7 and count up 5 more. 7 → 8 (1 more), 9 (2 more), 10 (3 more), 11 (4 more), 12 (5 more). Step 3: The total is 12. So, Liam now has 12 toy cars.

6. 17 + 2 = ? Answer: 19 Solution: We start with the problem: 17 + 2. The plus sign (+) tells us we need to combine the two numbers, 17 and 2, into a total sum. Since we are adding 2, we move 2 steps to the right from 17.
   Full step-by-step solution

   Step 1: We start with the problem: 17 + 2. Step 2: The plus sign (+) tells us we need to combine the two numbers, 17 and 2, into a total sum. Step 3: To add these numbers, we can think of starting at the number 17 on a number line. Step 4: Since we are adding 2, we move 2 steps to the right from 17. - First step: 17 + 1 = 18 - Second step: 18 + 1 = 19 Step 5: After moving 2 steps from 17, we arrive at the number 19. Step 6: Therefore, the sum of 17 and 2 is 19. Final Answer: 19

7. 2 + 5 = ? Answer: 7 Solution: Identify the numbers to be added. We have the number 2 and the number 5. The plus sign (+) tells us we need to perform addition.
   Full step-by-step solution

   Step 1: Identify the numbers to be added. We have the number 2 and the number 5. Step 2: Understand the operation. The plus sign (+) tells us we need to perform addition. Addition means combining the two quantities to find the total. Step 3: Combine the numbers. Start with the first number, 2. Then, count forward 5 more units. Counting forward: 2 -> 3 (1), 4 (2), 5 (3), 6 (4), 7 (5). Step 4: State the result. After counting forward 5 units from 2, we arrive at the number 7. Step 5: Final Answer. Therefore, 2 + 5 = 7.

8. 0 + 12 = ? Answer: 12 Solution: Identify the numbers in the problem. We are adding 0 and 12. Recall the property of zero in addition.
   Full step-by-step solution

   Step 1: Identify the numbers in the problem. We are adding 0 and 12. Step 2: Recall the property of zero in addition. Adding zero to any number does not change the value of that number. This is called the Additive Identity Property. Step 3: Apply the property to the calculation. Since we are adding 0 to 12, the sum is simply 12. Step 4: Write the final answer. 0 + 12 = 12

9. 2 + 1 = ? Answer: 3 Solution: We are adding the numbers 2 and 1. Start with the first number: 2. We need to add the second number, which is 1.
   Full step-by-step solution

   We are adding the numbers 2 and 1. Step 1: Start with the first number: 2. Step 2: We need to add the second number, which is 1. Adding 1 means we count forward by 1 from 2. Step 3: Counting forward from 2: 2 → 3. Step 4: So, 2 + 1 = 3. Final answer: 3

10. 3 + 10 = ? Answer: 13 Solution: We are adding the numbers 3 and 10. Write the problem clearly. 3 + 10 Start with the first number, 3.
    Full step-by-step solution

    We are adding the numbers 3 and 10. Step 1: Write the problem clearly. 3 + 10 Step 2: Start with the first number, 3. If you count 10 more from 3, you get: 3 → 4 (1 more), 5 (2 more), 6 (3 more), 7 (4 more), 8 (5 more), 9 (6 more), 10 (7 more), 11 (8 more), 12 (9 more), 13 (10 more). Step 3: Alternatively, you can think of it as combining the two numbers directly: 3 + 10 = 13. Step 4: Check the result: 10 + 3 is the same as 3 + 10 because addition is commutative. 10 + 3 = 13, so the answer is consistent. Final Answer: 13