Subtraction Within 20

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Answer Key & Explanations

Subtraction Within 20 · Grade 1 · Worksheet 3

1. 3 - 1 = ? Answer: 2 Solution: We start with the problem: 3 - 1 Understand the operation. The minus sign means we are subtracting 1 from 3. Count backwards if it helps.
   Full step-by-step solution

   We start with the problem: 3 - 1 Step 1: Understand the operation. The minus sign means we are subtracting 1 from 3. Step 2: Count backwards if it helps. Begin at the number 3. Move one step to the left (down) on the number line: 3 → 2 Step 3: Verify the result. If we have 3 objects and remove 1, we have 2 objects left. So 3 - 1 = 2. Final answer: 2

2. 13 - 10 = ? Answer: 3 Solution: We start with the problem: 13 - 10. We are subtracting 10 from 13. This means we are taking away 10 items from a total of 13 items.
   Full step-by-step solution

   We start with the problem: 13 - 10. Step 1: Understand the operation. We are subtracting 10 from 13. This means we are taking away 10 items from a total of 13 items. Step 2: Perform the subtraction. We can think of 13 as 10 + 3. If we remove 10 from 13, we are left with 3. Step 3: Verify the calculation. 13 - 10 = 3, because 10 + 3 = 13, so removing 10 leaves 3. Step 4: Final answer. Therefore, 13 - 10 = 3.

3. 7 - 7 = ? Answer: 0 Solution: Start with the given problem: 7 - 7. Subtraction means taking away a certain quantity from another. Here, we are taking away 7 from 7.
   Full step-by-step solution

   Step 1: Start with the given problem: 7 - 7. Step 2: Understand the operation. Subtraction means taking away a certain quantity from another. Here, we are taking away 7 from 7. Step 3: Visualize the process. If you have 7 objects and you remove all 7 of them, you are left with no objects. Step 4: Perform the calculation. Subtracting a number from itself always results in zero. Step 5: Write the final answer. 7 - 7 = 0

4. 6 - 2 = ? Answer: 4 Solution: Start with the number 6. The problem asks us to subtract 2 from 6. Subtraction means we are taking away a quantity.
   Full step-by-step solution

   Step 1: Start with the number 6. Step 2: The problem asks us to subtract 2 from 6. Subtraction means we are taking away a quantity. Step 3: To visualize this, if you have 6 objects and remove 2 of them, you count how many are left. Step 4: Removing 1 object from 6 leaves 5 objects. Step 5: Removing a second object from 5 leaves 4 objects. Step 6: Therefore, 6 minus 2 equals 4. Final Answer: 4

5. 12 - 11 = ? Answer: 1 Solution: We are solving: 12 - 11 = ? We are subtracting 11 from 12. Write the numbers vertically in your mind for clarity: 12 - 11 Subtract the ones place first.
   Full step-by-step solution

   We are solving: 12 - 11 = ? Step 1: Understand the operation. We are subtracting 11 from 12. Step 2: Write the numbers vertically in your mind for clarity: 12 - 11 Step 3: Subtract the ones place first. The ones place of 12 is 2. The ones place of 11 is 1. 2 - 1 = 1. Write down 1 in the ones place of the answer. Step 4: Subtract the tens place. The tens place of 12 is 1. The tens place of 11 is 1. 1 - 1 = 0. Write down 0 in the tens place of the answer. Step 5: Combine the digits. The tens digit is 0, so we don't write it in front. The result is simply 1. Step 6: Check by addition. If 12 - 11 = 1, then 1 + 11 should equal 12. 1 + 11 = 12, which is correct. Final answer: 1

6. 14 - 1 = ? Answer: 13 Solution: We start with the problem: 14 - 1 = ? We are subtracting 1 from 14. Subtraction means we take away a certain amount from the starting number.
   Full step-by-step solution

   We start with the problem: 14 - 1 = ? Step 1: Understand the operation. We are subtracting 1 from 14. Subtraction means we take away a certain amount from the starting number. Step 2: Begin with the number 14. We can think of 14 as 1 ten and 4 ones, or simply as the whole number 14. Step 3: Remove 1 from 14. If we take away 1 from 14, we count one number backward from 14. So: 14, then 13. Step 4: Verify by addition. We know that subtraction is the inverse of addition. If 14 - 1 = 13, then 13 + 1 should equal 14. Check: 13 + 1 = 14, which is correct. Step 5: Conclusion. Therefore, 14 - 1 = 13. ANSWER: 13

7. 9 - 3 = ? Answer: 6 Solution: We start with the problem: 9 - 3 Understand the operation. The minus sign means we are subtracting 3 from 9. Count backwards if needed.
   Full step-by-step solution

   We start with the problem: 9 - 3 Step 1: Understand the operation. The minus sign means we are subtracting 3 from 9. Step 2: Count backwards if needed. From 9, count down 3 steps: 9 → 8 (1 step), 8 → 7 (2 steps), 7 → 6 (3 steps). Step 3: Verify by addition. If 9 - 3 = 6, then adding 3 to 6 should give 9. Check: 6 + 3 = 9, which is correct. Step 4: Final answer. Therefore, 9 - 3 = 6.

8. 15 - 3 = ? Answer: 12 Solution: We start with the problem: 15 - 3 Understand the operation. We are subtracting 3 from 15. This means we take away 3 from the total of 15.
   Full step-by-step solution

   We start with the problem: 15 - 3 Step 1: Understand the operation. We are subtracting 3 from 15. This means we take away 3 from the total of 15. Step 2: Break 15 into parts if it helps. 15 is the same as 10 + 5. So, 15 - 3 = (10 + 5) - 3. Step 3: Subtract from the ones place first. From the 5 ones, subtract 3 ones: 5 - 3 = 2. Step 4: Combine with the remaining 10. We still have the 10 from earlier, so: 10 + 2 = 12. Step 5: Final answer. Therefore, 15 - 3 = 12.

9. 13 - 2 = ? Answer: 11 Solution: Start with the number 13. We need to subtract 2 from 13. This means we take away 2 units from 13.
   Full step-by-step solution

   Let's solve 13 - 2 step by step. Step 1: Start with the number 13. Step 2: We need to subtract 2 from 13. This means we take away 2 units from 13. Step 3: Think of 13 as 10 + 3. If we take away 2 from the 3, we have 3 - 2 = 1 left. Step 4: Now we combine what is left: 10 + 1 = 11. So, 13 - 2 = 11.

10. 5 - 0 = ? Answer: 5 Solution: Start with the number 5. The problem says to subtract 0 from 5. Subtracting 0 means taking away nothing.
    Full step-by-step solution

    Step-by-step solution: Step 1: Start with the number 5. Step 2: The problem says to subtract 0 from 5. Subtracting 0 means taking away nothing. Step 3: When you take away nothing from a quantity, the quantity remains unchanged. Step 4: Therefore, 5 minus 0 equals 5. Final answer: 5