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Find missing numbers on number line

Class 1 Class 2 CBSE UP Board

📘 What's inside:

Concept 1 — What is a Missing Number on a Number Line?

Sometimes a number line is shown with some numbers missing. A dashed box sits in place of the missing number. Our job is to find what belongs there.

The key idea is simple: on any number line, the gap between neighbouring numbers is always equal. This equal gap is called the step size. Once we know the step size, we can find any missing number.

▶ How to Find a Missing Number
  • Look at the numbers that are given on the number line.
  • Find the step size — subtract any two neighbouring known numbers.
  • Add the step to the number before the blank, or subtract from the number after it.
  • Always verify using both directions — your answer must fit perfectly.

Click the dashed boxes below to reveal the missing numbers:

0, 1, 2, 3, 4, 5, ?, 7, 8, 9, 10 Tap the dashed box to reveal Step size = 1 — find the missing number
⚠ Common Mistake

Many students guess the missing number without checking the step size first. Always find the step size before filling any blank. If you add and the result does not match the next known number, recheck the step.

▶ Solved Example 1
Find the missing number. Click the box to check your answer.
0, 1, 2, 3, 4, 5, ?, 7, 8, 9, 10
  1. 1Look at the given numbers: 0, 1, 2, 3, 4, 5, ?, 7, 8, 9, 10.
  2. 2Find step size: 1 − 0 = 1.
  3. 3Number before blank = 5. Add step: 5 + 1 = 6.
  4. 4Verify: 7 − 1 = 6. Both methods agree.
5, 6, 7 Step = 1 — Missing number = 6
Missing number = 6
▶ Solved Example 2
Find the missing number:  3, 5, 7, ?, 11, 13
  1. 1Step size: 5 − 3 = 2. This is a counting-by-2s sequence.
  2. 2Number before blank = 7. Add step: 7 + 2 = 9.
  3. 3Verify: 11 − 2 = 9. Confirmed.
7, 9, 11 Step = 2 — Missing number = 9
Missing number = 9   (Step size = 2)

✍ Practice — Concept 1 — Click the box to reveal the answer

Q1 Find the missing number:   0, 1, 2, ?, 4, 5 ▼
Answer — tap the box
2, ?, 4 Step = 1
Step size: 1 − 0 = 1.
Before blank = 2. Add step: 2 + 1 = 3. Verify: 4 − 1 = 3.
Q2 Find the missing number:   10, 12, ?, 16, 18 ▼
Answer — tap the box
12, ?, 16 Step = 2
Step size: 12 − 10 = 2.
12 + 2 = 14. Verify: 16 − 2 = 14.
Q3 Find the missing number:   1, 3, 5, 7, ?, 11 ▼
Answer — tap the box
7, ?, 11 Step = 2 (odd numbers)
Step = 2. 7 + 2 = 9. Verify: 11 − 2 = 9.
Q4 A student says the missing number in 4, 8, ?, 16, 20 is 11. Is this correct? Find the right answer. ▼
Answer — tap the box
8, ?, 16 Step = 4 — not 3!
No, 11 is wrong.
Step size: 8 − 4 = 4. This is counting by 4s.
8 + 4 = 12. Verify: 16 − 4 = 12.

Concept 2 — Finding the Step Size

The step size is the key to finding any missing number. Let us practise finding step sizes in different situations.

▶ Rules for Finding Step Size
  • If two neighbouring numbers are known: step = bigger − smaller.
  • If numbers are two positions apart with one blank between: step = difference ÷ 2.
  • If numbers are three positions apart with two blanks: step = difference ÷ 3.
  • Always verify the step by checking it works for every pair in the sequence.
▶ Solved Example 3
Find the step size and missing number:  0, ?, 10, 15, 20
  1. 1Two known neighbours: 10 and 15. Step = 15 − 10 = 5.
  2. 2Verify: 20 − 15 = 5. Step confirmed = 5.
  3. 3Blank comes after 0. Add step: 0 + 5 = 5.
  4. 4Verify: 10 − 5 = 5. Confirmed.
0, 5, 10, 15, 20 Step = 5 — Missing = 5
Step size = 5   Missing number = 5
▶ Solved Example 4
Find the step size and missing number:  6, ?, 14, 18, 22
  1. 1Two known neighbours: 14 and 18. Step = 18 − 14 = 4.
  2. 2Verify: 22 − 18 = 4. Step confirmed.
  3. 3Blank comes after 6. Add step: 6 + 4 = 10.
  4. 4Verify: 14 − 4 = 10. Confirmed.
6, 10, 14, 18, 22 Step = 4 — Missing = 10
Step size = 4   Missing number = 10

✍ Practice — Concept 2 — Click the box to reveal

Q5 Find step size and missing number:   5, ?, 15, 20, 25 ▼
Answer — tap the box
5, ?, 15 Step = 5
Step: 20 − 15 = 5.   5 + 5 = 10. Verify: 15 − 5 = 10.
Q6 Find step size and missing number:   8, 12, ?, 20, 24 ▼
Answer — tap the box
12, ?, 20 Step = 4
Step: 12 − 8 = 4.   12 + 4 = 16. Verify: 20 − 4 = 16.
Q7 What is the step size if a number line goes: 3, 6, 9, ?, 15? ▼
Answer — tap the box
9, ?, 15 Step = 3 (counting by 3s)
Step: 6 − 3 = 3.   9 + 3 = 12. Verify: 15 − 3 = 12.

Concept 3 — Finding Multiple Missing Numbers

Sometimes more than one number is missing. We use the same method — find the step first, then fill each blank one at a time from left to right.

▶ When Multiple Numbers are Missing
  • Find two consecutive known numbers and calculate the step size.
  • If no two neighbours are known, use numbers that are 2 steps apart and halve the gap.
  • Fill blanks one at a time, left to right, using the step each time.
  • Always check your last filled number against the next known number.
▶ Solved Example 5
Find all missing numbers:  5, ?, 9, ?, 13, 15
  1. 1Known neighbours: 13 and 15. Step = 15 − 13 = 2.
  2. 2Verify: 9 to ? to 13 with step 2: 9 + 2 = 11? But 11 + 2 = 13. Yes, step = 2.
  3. 3First blank: 5 + 2 = 7. Verify: 9 − 2 = 7.
  4. 4Second blank: 9 + 2 = 11. Verify: 13 − 2 = 11.
5, 7, 9, 11, 13, 15 Step = 2 — Missing = 7 and 11
Missing numbers = 7 and 11
▶ Solved Example 6
Find all missing numbers:  0, ?, ?, 15, ?, 25
  1. 1Known: 15 and 25, with one blank between = 2 positions apart. Step = (25 − 15) ÷ 2 = 5.
  2. 2Verify: 0 to 15 with 2 blanks = 3 steps. 15 ÷ 3 = 5. Confirmed.
  3. 3First blank: 0 + 5 = 5. Second blank: 5 + 5 = 10. Check: 15 − 5 = 10.
  4. 4Third blank: 15 + 5 = 20. Check: 25 − 5 = 20.
0, 5, 10, 15, 20, 25 Step = 5 — Missing = 5, 10 and 20
Missing numbers = 5, 10 and 20

✍ Practice — Concept 3 — Click each box to reveal

Q8 Find all missing numbers:   2, ?, 6, ?, 10 ▼
Answer — tap each box
2, ?, 6, ?, 10 Step = 2
Step = 2.   2+2=4   6+2=8.
Q9 Find all missing numbers:   20, ?, ?, ?, 40 ▼
Answer — tap each box
20, ?, ?, ?, 40 Step = 5
3 blanks between 20 and 40 = 4 steps. 20 ÷ 4 = 5.
25, 30, 35.
Q10 Find all missing numbers:   0, ?, ?, 9, ?, 15 ▼
Answer — tap each box
0, ?, ?, 9, ?, 15 Step = 3
15 − 9 = 6, one blank = 2 steps. 6 ÷ 2 = 3.
3, 6, 12.

Concept 4 — Missing Numbers in Skip Counting Sequences

When a number line uses skip counting by 2s, 5s or 10s, the step size is already known. Simply apply it directly.

▶ Known Step Sizes
  • Counting by 2s — step = 2. Numbers are always even or all odd.
  • Counting by 5s — step = 5. Numbers always end in 0 or 5.
  • Counting by 10s — step = 10. Numbers always end in 0.
▶ Solved Example 7
Fill in (counting by 2s):  0, 2, ?, 6, ?, 10, ?, 14
  1. 1Counting by 2s. Step = 2.
  2. 2First blank: 2 + 2 = 4. Check: 6 − 2 = 4.
  3. 3Second blank: 6 + 2 = 8. Check: 10 − 2 = 8.
  4. 4Third blank: 10 + 2 = 12. Check: 14 − 2 = 12.
0, 2, 4, 6, 8, 10, 12, 14 Counting by 2s — Missing = 4, 8, 12
Missing numbers = 4, 8 and 12
▶ Solved Example 8
Fill in (counting by 10s):  10, ?, 30, ?, ?, 60
  1. 1Counting by 10s. Step = 10. Numbers end in 0.
  2. 2First blank: 10 + 10 = 20. Check: 30 − 10 = 20.
  3. 3Second blank: 30 + 10 = 40.
  4. 4Third blank: 40 + 10 = 50. Check: 60 − 10 = 50.
10, 20, 30, 40, 50, 60 Counting by 10s — Missing = 20, 40, 50
Missing numbers = 20, 40 and 50

✍ Practice — Concept 4 — Click each box to reveal

Q11 Fill in (counting by 5s):   5, 10, ?, 20, ?, 30 ▼
Answer — tap each box
10, ?, 20, ?, 30 Step = 5
10 + 5 = 15.   20 + 5 = 25.
Q12 Fill in (counting by 2s):   ?, 4, 6, ?, 10, ? ▼
Answer — tap each box
?, 4, 6, ?, 10, ? Step = 2
4 − 2 = 2.   6 + 2 = 8.   10 + 2 = 12.
Q13 Fill in (counting by 10s):   ?, 20, ?, 40, 50, ? ▼
Answer — tap each box
?, 20, ?, 40, 50, ? Step = 10
20 − 10 = 10.   20 + 10 = 30.   50 + 10 = 60.

Concept 5 — Missing Numbers on Larger Number Lines (up to 100)

The same method works for larger numbers up to 100. The step size may be 5, 10 or 20. Read the given numbers carefully before filling any blank.

⚠ Watch Out

On a number line showing 0 to 100, each visible tick mark may represent a step of 10 or even 20. Always read the given numbers carefully and find the actual step size before filling any blank.

▶ Solved Example 9
A number line shows:  0, 10, ?, 30, ?, 50, 60, ?, 80, 90, 100. Find all missing numbers.
  1. 1Step: 10 − 0 = 10. Counting by 10s.
  2. 2First blank (between 10 and 30): 10 + 10 = 20.
  3. 3Second blank (between 30 and 50): 30 + 10 = 40.
  4. 4Third blank (between 60 and 80): 60 + 10 = 70.
10, 20, 30, 40, 50, 60, 70, 80 Step = 10 — Missing = 20, 40, 70
Missing numbers = 20, 40 and 70
▶ Solved Example 10
Find the missing numbers:  25, ?, 45, 55, ?, 75
  1. 1Known neighbours: 45 and 55. Step = 55 − 45 = 10.
  2. 2First blank: 25 + 10 = 35. Check: 45 − 10 = 35.
  3. 3Second blank: 55 + 10 = 65. Check: 75 − 10 = 65.
25, 35, 45, 55, 65, 75 Step = 10 — Missing = 35 and 65
Missing numbers = 35 and 65

✍ Practice — Concept 5 — Click each box to reveal

Q14 Find missing numbers:   0, ?, 20, 30, ?, 50 ▼
Answer — tap each box
0, ?, 20, 30, ?, 50 Step = 10
Step = 10.   0+10=10.   30+10=40.
Q15 Find missing numbers:   30, ?, 50, ?, 70, ? ▼
Answer — tap each box
30, ?, 50, ?, 70, ? Step = 10
Step = 10.   40, 60, 80.
Q16 Riya fills a number line: 40, ?, ?, 70, ?, 90. Help her find the missing numbers. ▼
Answer — tap each box
40, ?, ?, 70, ?, 90 Step = 10
Step: 90 − 70 = 20, one blank = 2 steps, 20 ÷ 2 = 10.
50, 60, 80.
★ Key Points to Remember
  • The gap between every neighbouring pair on a number line is always equal.
  • Always find the step size first before filling any blank.
  • Add the step to the number before the blank, or subtract from the number after it.
  • Always verify your answer using both directions.
  • By 2s → step 2.   By 5s → step 5.   By 10s → step 10.

Exam Style — Full Topic

5 Questions on Finding Missing Numbers

Q1 Find the missing number:   7, 9, 11, ?, 15, 17 ▼
Answer — tap the box
11, ?, 15 Step = 2 (odd numbers)
Step: 9 − 7 = 2.   11 + 2 = 13. Verify: 15 − 2 = 13.
Q2 Find all missing numbers:   0, ?, 10, ?, 20 ▼
Answer — tap each box
0, ?, 10, ?, 20 Step = 5
10 − 0 = 10, one blank = 2 steps, 10 ÷ 2 = 5.
0+5=5.   10+5=15.
Q3 A number line shows multiples of 5: 15, 20, ?, ?, 35, 40. Find the missing numbers. ▼
Answer — tap each box
20, ?, ?, 35 Step = 5 (multiples of 5)
Step: 20 − 15 = 5.
20+5=25.   25+5=30.
Q4 Find all missing numbers:   40, ?, ?, 70, ?, 90 ▼
Answer — tap each box
40, ?, ?, 70, ?, 90 Step = 10
Step: 90 − 70 = 20, one blank = 2 steps, 20 ÷ 2 = 10.
50, 60, 80.
Q5 Riya writes: 6, ?, 10, 12, ?, 16. Help her fill the blanks and name the type of sequence. ▼
Answer — tap each box
6, ?, 10, 12, ?, 16 Step = 2 (even numbers)
Step: 12 − 10 = 2.   6+2=8.   12+2=14.
This is a skip counting by 2s sequence (even numbers).
📄 Free Worksheet

Practise finding missing numbers on number lines with step sizes 1, 2, 5 and 10 with our free printable worksheet. No login required.

► Open Free Worksheet
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