Solved Exercises on Addition/Subtraction Practice in Grade 2

Master addition and subtraction within 100: number sense, mental math, regrouping, word problems, and problem-solving strategies through these 5 detailed exercises.

Solution: Exercises 1 to 3
1 Mental Math Practice
Exercise 1
Solve mentally:
23 + 15 = ? and 47 - 12 = ?
Definition:

Mental Math: Calculating in your head without paper or calculator

Mental Math Strategy:
  1. Add tens first, then ones
  2. Use number bonds you know
  3. Round numbers if helpful
  4. Check your answer mentally
Problem
23 + 15
Break Down
20+3+10+5
Result
38
Step 1: Separate tens and ones

23 = 20 + 3 and 15 = 10 + 5

Step 2: Add tens together

20 + 10 = 30

Step 3: Add ones together

3 + 5 = 8

Step 4: Combine results

30 + 8 = 38

23 + 15 = 38
Final answer:

23 + 15 = 38 and 47 - 12 = 35

Applied rules:

• Place Value: Work with tens and ones separately

• Decomposition: Break numbers into tens and ones

• Regrouping: Combine partial sums

23
20 + 3
+
+
15
10 + 5
=
=
38
30 + 8
2 Regrouping Practice
Exercise 2
Solve with regrouping:
46 + 28 = ? and 53 - 17 = ?
Definition:

Regrouping: Moving numbers from one place value to another (borrowing/carrying)

Problem
46 + 28
Regroup
46+20+8
Result
74
Step 1: Add ones column first

6 + 8 = 14 (more than 10, so we regroup)

Step 2: Carry the ten

Write down 4, carry over 1 ten to the tens column

Step 3: Add tens column

4 + 2 + 1 (carried) = 7 tens

Step 4: Write final answer

7 tens and 4 ones = 74

46 + 28 = 74
Final answer:

46 + 28 = 74 and 53 - 17 = 36

Applied rules:

• Regrouping Rule: When ones exceed 9, carry to tens

• Borrowing Rule: When subtracting, borrow from higher place

• Place Value: Keep digits in correct columns

46
4 tens + 6 ones
+
+
28
2 tens + 8 ones
=
=
74
6 ones → 1 ten + 4 ones
3 Word Problem Practice
Exercise 3
Sarah has 34 stickers. She gets 27 more for her birthday. Then she gives 15 to her friend. How many stickers does Sarah have now?
Definition:

Word Problem: A math problem presented in sentence form requiring analysis and calculation

Problem
34 + 27 - 15
Calculate
61 - 15
Result
46
Step 1: Identify what happens first

Sarah starts with 34 stickers and gets 27 more

Step 2: Add the initial amount

34 + 27 = 61 stickers after birthday

Step 3: Account for what happens next

She gives 15 stickers to her friend

Step 4: Subtract the given stickers

61 - 15 = 46 stickers remaining

Step 5: State the final answer

Sarah has 46 stickers now

46 stickers
Final answer:

Sarah has 46 stickers now.

Applied rules:

• Sequence: Follow the order of events in the problem

• Keywords: "gets" means add, "gives" means subtract

• Verification: Check if answer makes sense in context

Starting Amount: 34 stickers
Gets More: 34 + 27 = 61 stickers
Gives Away: 61 - 15 = 46 stickers
Final Answer: 46 stickers
Rules and methods, laws,...
a + b = c → c - a = b
Inverse Operations
Commutative
a + b = b + a
Order doesn't matter
Associative
(a + b) + c = a + (b + c)
Grouping doesn't matter
Identity
a + 0 = a
Adding zero doesn't change
Key definitions:

Addition: Combining two or more numbers to get a total

Subtraction: Taking away one number from another

Regrouping: Moving numbers between place values when necessary

Word Problem: A mathematical problem presented in a real-world context

Problem-Solving Steps:
  1. Read Carefully: Understand what the problem is asking
  2. Identify Numbers: Find the important numbers in the problem
  3. Choose Operation: Decide whether to add or subtract
  4. Solve: Perform the calculation
  5. Check: Verify if the answer makes sense
Tip 1: Look for keywords like "total," "altogether," "more" (addition) and "left," "less," "gave away" (subtraction).
Tip 2: Always check your answer by using the opposite operation.
Tip 3: Draw pictures or use objects to visualize the problem if needed.
Solution: Exercises 4 to 5
4 Missing Number Problems
Exercise 4
Find the missing numbers:
25 + ? = 43 and ? - 18 = 24
Definition:

Missing Number: An unknown value in an equation that needs to be found

Problem
25 + ? = 43
Solve
43 - 25
Result
18
Step 1: Understand the equation

25 + ? = 43 means we need to find what to add to 25 to get 43

Step 2: Use inverse operation

To find the missing addend, subtract: 43 - 25 = 18

Step 3: Verify the answer

Check: 25 + 18 = 43 ✓

Step 4: Solve the second equation

? - 18 = 24 means we need to find what minus 18 equals 24

Step 5: Use inverse operation

To find the minuend, add: 24 + 18 = 42

? = 18 and ? = 42
Final answer:

25 + 18 = 43 and 42 - 18 = 24

Applied rules:

• Inverse Operations: Addition and subtraction undo each other

• Missing Addend: Subtract known addend from sum

• Missing Minuend: Add subtrahend to difference

5 Mixed Operations Challenge
Exercise 5
Solve in order: 56 - 23 + 14 - 8 = ?
Definition:

Mixed Operations: Calculations involving both addition and subtraction

Problem
56 - 23 + 14 - 8
Left to Right
33 + 14 - 8
Result
39
Step 1: Follow order of operations (left to right)

56 - 23 = 33

Step 2: Continue with next operation

33 + 14 = 47

Step 3: Continue with final operation

47 - 8 = 39

Step 4: Verify the result

Work backwards or use estimation to check

56 - 23 + 14 - 8 = 39
Final answer:

56 - 23 + 14 - 8 = 39

Applied rules:

• Order of Operations: Perform operations left to right

• Same Priority: Addition and subtraction have equal priority

• Sequential Processing: One operation at a time

Add list of laws, methods, rules, definitions, expressions,.... Generate well SEO title for this section
a + b = b + a
Commutative Property
Key definitions:

Addition: Combining quantities to find a total

Subtraction: Finding the difference or taking away

Regrouping: Moving from one place value to another

Mental Math: Calculating without writing down steps

Complete methodology:
  1. Read the problem carefully and identify what operation is needed
  2. Estimate the answer to check reasonableness
  3. Choose the right strategy: counting on, making ten, place value, etc.
  4. Perform the calculation step by step
  5. Check your work by using inverse operations
Tip 1: Use number lines to visualize addition and subtraction.
Tip 2: Practice with manipulatives like base-ten blocks to understand place value.
Tip 3: Always estimate first to catch major calculation errors.
Tip 4: Check subtraction by adding your answer to the smaller number.
Common errors: Misreading place values, forgetting to regroup, incorrect operation choice.
Exam preparation: Practice mental math, master regrouping, solve word problems.
Properties to know by heart:

• Commutative: a + b = b + a

• Identity: a + 0 = a

• Inverse: a + b = c means c - a = b

• Associative: (a + b) + c = a + (b + c)

Exercise with Visualization: Number Patterns
Exercise 6: Pattern Recognition
Observe patterns in addition/subtraction:
Adding 10: 5, 15, 25, 35...
Subtracting 5: 50, 45, 40, 35...
Alternating +3/-2: 10, 13, 11, 14, 12...

Analysis: Recognizing patterns helps with mental math and understanding number relationships.

  • Adding 10: Only tens place changes
  • Subtracting 5: Decreases by 5 each time
  • Alternating operations: Follow the sequence pattern

Questions & Answers

Question: I get confused when I need to regroup in subtraction. How do I know when to borrow?

Answer: Great question! You need to borrow (regroup) in subtraction when the top number in a column is smaller than the bottom number:

  • In 52 - 18, when looking at the ones place, 2 is smaller than 8
  • You need to borrow 1 ten from the tens place (5 becomes 4)
  • The borrowed 1 ten becomes 10 ones, so 2 becomes 12
  • Now you can subtract: 12 - 8 = 4

The rule is: "Top is less? Go next door, borrow 10 more!"

Practice with base-ten blocks to visualize this concept!

Question: How do I know if I should add or subtract in word problems?

Answer: Look for key words that indicate the operation:

  • Addition words: total, altogether, combined, more, increased by, sum
  • Subtraction words: left, remaining, difference, less, decreased by, gave away
  • Context matters: Getting something means add, losing something means subtract

Example: "Sarah had 10 apples and bought 5 more" → add (10 + 5)

Example: "Tom had 15 marbles and lost 3" → subtract (15 - 3)

Always read the entire problem to understand what's happening!

Question: What's the easiest way to do mental math quickly?

Answer: Here are effective mental math strategies:

  • Make 10 first: For 8 + 5, think 8 + 2 = 10, then 10 + 3 = 13
  • Add tens first: For 24 + 35, do 20 + 30 = 50, then 4 + 5 = 9, so 50 + 9 = 59
  • Use doubles: Know 6 + 6 = 12, so 6 + 7 = 13
  • Round and adjust: For 38 + 27, think 40 + 25 = 65

Practice these strategies daily with different numbers to build fluency.

The more you practice, the faster your mental math will become!