Solved Exercises on Counting to 100 by Tens in Grade 2

Master counting to 100 by tens: skip counting, place value understanding, and number sequence recognition through these 5 detailed exercises.

Solution: Exercises 1 to 3
1 Skip Counting by Tens
Exercise 1
Fill in the missing numbers in this pattern:
10, 20, 30, ___, 50, 60, 70, ___, 90, 100
Definition:

Skip counting by tens: Adding 10 to each number to get the next number in the sequence

Skip counting method:
  1. Identify the pattern (adding 10 each time)
  2. Add 10 to the previous number to find the next number
  3. Continue the pattern until the end
Pattern
10, 20, 30, ?, 50, 60, 70, ?, 90, 100
Rule
Add 10
Solution
40, 80
Step 1: Identify the pattern

20 - 10 = 10, so we're adding 10 each time

Step 2: Find the first missing number

30 + 10 = 40

Step 3: Find the second missing number

70 + 10 = 80

10, 20, 30, 40, 50, 60, 70, 80, 90, 100
Final answer:

The missing numbers are 40 and 80

Applied rules:

• Pattern Recognition: Identify the constant difference between consecutive numbers

• Place Value: Only the tens digit changes when skip counting by 10s

• Consistency: The same rule applies to all numbers in the sequence

2 Skip Counting Backwards by Tens
Exercise 2
Count backwards by 10s starting from 100:
100, 90, 80, ___, 60, 50, 40, ___, 20, 10
Definition:

Skip counting backwards by tens: Subtracting 10 from each number to get the next number in the sequence

Pattern
100, 90, 80, ?, 60, 50, 40, ?, 20, 10
Rule
Subtract 10
Solution
70, 30
Step 1: Identify the pattern

100 - 90 = 10, so we're subtracting 10 each time

Step 2: Find the first missing number

80 - 10 = 70

Step 3: Find the second missing number

40 - 10 = 30

100, 90, 80, 70, 60, 50, 40, 30, 20, 10
Final answer:

The missing numbers are 70 and 30

Applied rules:

• Backward Counting: Subtract the same amount each time

• Place Value: Only the tens digit changes when skip counting by 10s

• Consistency: The same operation applies to all numbers in the sequence

3 Counting by Tens from Different Starting Points
Exercise 3
Complete the sequence counting forward by 10s starting from 25:
25, 35, 45, 55, ___, 75, 85, ___
Definition:

Skip counting by tens from any starting point: Adding 10 to each number to continue the sequence

Pattern
25, 35, 45, 55, ?, 75, 85, ?
Rule
Add 10
Solution
65, 95
Step 1: Identify the pattern

35 - 25 = 10, so we're adding 10 each time

Step 2: Find the first missing number

55 + 10 = 65

Step 3: Find the second missing number

85 + 10 = 95

Step 4: Verify the sequence

65 - 55 = 10 ✓, confirming our pattern

25, 35, 45, 55, 65, 75, 85, 95
Final answer:

The missing numbers are 65 and 95

Applied rules:

• Pattern Recognition: Identify the constant difference (10) between consecutive numbers

• Place Value: Only the tens digit changes when skip counting by 10s

• Verification: Check that the pattern holds between known numbers

Rules and methods, laws,...
Skip Counting by Tens: Start + 10 × Position
Number Sequence Formula
Skip by Tens
Add 10
Pattern: 10, 20, 30, 40, 50...
Skip by Tens
Subtract 10
Pattern: 100, 90, 80, 70, 60...
Any Starting Point
Add 10
Pattern: 25, 35, 45, 55...
Key definitions:

Skip Counting by Tens: Counting by a number 10 (like 10, 20, 30, etc.)

Place Value: Understanding tens and ones in 2-digit numbers

Number Pattern: A sequence of numbers that follows a specific rule

Transition Point: When counting reaches a boundary (like 90 to 100) and place values change

Complete methodology:
  1. Analyze the sequence: Look at the first few numbers to identify the pattern
  2. Determine the step: Calculate the difference between consecutive numbers
  3. Apply the rule: Use the identified pattern to fill in missing numbers
  4. Verify your answer: Check that the pattern continues consistently
Tip 1: When counting by 10s, only the tens digit changes (20, 30, 40).
Tip 2: When the tens digit is 9, the next number crosses to the next hundred (90→100).
Tip 3: Use your fingers or count aloud to check your pattern.
Tip 4: Practice counting by 10s from different starting points (25, 37, 43, etc.).

Common errors: Forgetting to change the correct digit, miscounting the step, not recognizing the pattern.
Key notes: Skip counting by 10s is the foundation for understanding multiplication by 10.
Rules to know by heart:

• Skip by 10s: Add 10 each time (tens digit increases by 1)

• Skip by 10s backwards: Subtract 10 each time (tens digit decreases by 1)

• When tens digit is 9: Adding 10 increases hundreds digit (90→100)

• Pattern consistency: The same rule applies throughout the sequence

• Place value: Only the tens digit changes unless crossing a boundary

Solution: Exercises 4 to 5
4 Skip Counting by Tens Across Boundaries
Exercise 4
Identify the pattern and continue the sequence:
90, 100, 110, 120, 130, 140, 150, ___
Definition:

Skip counting by tens across hundreds boundary: Continuing the pattern when crossing 100

Sequence
90→100→110→120→130→140→150→?
Pattern
Add 10
Next
160
Step 1: Analyze the differences

100-90=10, 110-100=10, 120-110=10, 130-120=10, 140-130=10, 150-140=10

Step 2: Notice the transition point

From 90 to 100, the pattern continues smoothly across the hundreds boundary

Step 3: Apply the pattern

After 150, the next number is 150 + 10 = 160

Step 4: Calculate the next number

150 + 10 = 160

Next number: 160
Final answer:

The next number in the sequence is 160

Applied rules:

• Pattern Analysis: Calculate differences between consecutive numbers

• Boundary Crossing: The pattern continues across hundreds boundaries

• Consistency Check: Verify the pattern continues correctly

5 Place Value Understanding
Exercise 5
What comes next in this sequence?
75, 85, 95, 105, 115, 125, 135, 145, 155, 165, 175, ___
Definition:

Place value transition: Understanding how numbers change when skip counting by 10s

Sequence
75→85→95→105→...→175→?
Rule
Add 10
Result
185
Step 1: Identify the pattern

Each number increases by 10 (85-75=10, 95-85=10, etc.)

Step 2: Understand place value transition

From 95 to 105, the tens digit goes from 9 to 0, and the hundreds digit increases

Step 3: Calculate the next number

175 + 10 = 185 (the 5 in tens place increases by 1)

Step 4: Verify the pattern

175 + 10 = 185, maintaining the skip counting by 10s pattern

Next number: 185
Final answer:

The next number in the sequence is 185

Applied rules:

• Place Value Understanding: Know how digits change when reaching 9 in any place

• Tens Transition: When tens reach 9 and add 10, hundreds increase

• Pattern Consistency: Maintain the same skip counting rule throughout

Detailed Summary: Counting to 100 by Tens
nth Term = Start + (n-1) × 10
Arithmetic Sequence Formula
Key definitions:

Skip Counting by Tens: Counting forward or backward by a consistent interval of 10

Place Value: Understanding that each digit position represents tens or ones

Number Pattern: A sequence of numbers that follows a predictable rule

Transition Point: When counting reaches a boundary (like 90 to 100) and place values change

Complete methodology:
  1. Observe the sequence: Look at the first few numbers to understand the starting point
  2. Calculate differences: Find the difference between consecutive numbers to determine the step
  3. Identify the pattern: Determine if it's skip counting by 10s
  4. Apply the rule: Use the identified step to continue the sequence
  5. Verify results: Check that the pattern continues consistently throughout
Tip 1: When skip counting by 10s, the last digit stays the same while the tens digit changes.
Tip 2: Practice counting by 10s starting from any number (not just multiples of 10).
Tip 3: Use your hands to count by 10s: 10, 20, 30, 40, etc. (each finger represents 10).
Tip 4: Practice counting forward and backward to strengthen number sense.
Common errors: Forgetting to carry over when reaching 9 in any place value, misidentifying the pattern, not maintaining consistency in the skip counting step.
Memory aids: Remember that skip counting by 10s changes only the tens digit (except at transition points).
Formulas to know by heart:

• Skip counting by 10s: Add 10 each time (10, 20, 30, 40...)

• Skip counting by 10s backwards: Subtract 10 each time (100, 90, 80, 70...)

• From any starting point: Add 10 each time (25, 35, 45, 55...)

• Boundary transition: When tens digit is 9, adding 10 increases hundreds digit (90→100)

• Pattern consistency: The same rule applies throughout the sequence

Exercise with Visualization: Skip Counting by Tens to 100
Exercise 6: Number Line Visualization
Visualize skip counting patterns on a number line:
Skip by 10s: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
Skip by 10s from 15: 15, 25, 35, 45, 55, 65, 75, 85, 95
10
20
30
40
50
60
70
80
90
100

Analysis: The visualization shows how skip counting creates evenly spaced intervals on the number line.

  • Skip by 10s: Consistent 10-unit jumps throughout the sequence
  • Pattern consistency: Equal distances between consecutive numbers
  • Place value: Only the tens digit changes in each step

Questions & Answers

Question: I don't understand why when I count from 90 by 10s, it goes 90, 100, 110. Why does the 90 become 00?

Answer: Great question! This happens because of place value rules:

  • In 90, the tens digit is 9 and the ones digit is 0
  • When you add 10 to 90, you're adding to the tens place: 9 tens + 1 ten = 10 tens
  • But 10 tens equals 1 hundred, so you carry the 1 to the hundreds place
  • This makes the tens digit go back to 0, and the hundreds digit increases from 0 to 1
  • The ones digit stays the same (0)

So: 90 + 10 = 100 (0 hundreds, 9 tens, 0 ones becomes 1 hundred, 0 tens, 0 ones)

Think of it like having 99 cents and adding 10 cents - you now have $1.09, not 9009 cents!

Question: How can I remember whether to add or subtract when skip counting?

Answer: Here are some helpful strategies to remember:

  • Forward counting: Going up (like climbing stairs) means adding
  • Backward counting: Going down (like going down stairs) means subtracting
  • Look for direction words: "forward," "up," "more" usually mean addition
  • Look for direction words: "backward," "down," "less" usually mean subtraction

For example: "Count forward by 10s" means add 10 each time. "Count backward by 10s" means subtract 10 each time.

Tip: Practice with a number line - moving right is adding, moving left is subtracting!

Question: What's the easiest way to learn skip counting by 10s? I keep getting confused.

Answer: Here are effective strategies for skip counting by 10s:

  • Use your hands: Count your fingers - each hand has 5 fingers, so 2 hands = 10, 4 hands = 20, etc.
  • Notice the pattern: The ones digit stays the same, only the tens digit changes
  • Connect to money: Dimes are worth 10 cents, so count dimes: 10¢, 20¢, 30¢, 40¢...
  • Count in groups: Think of sets of 10: 1 set = 10, 2 sets = 20, 3 sets = 30, etc.

Practice saying: "10, 20, 30, 40, 50, 60..." rhythmically. The rhythm helps your brain remember the pattern!

Start with smaller ranges (like 10-50) before attempting larger ranges (like 10-100).