Factors in Number System & Arithmatics
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Factors in Mathematics – Definition, Steps, Examples & 20 MCQs with Solutions

⭐ FACTORS — Detailed Explanation

A factor of a number is an integer that divides the number exactly without leaving any remainder.
In other words:

  • If a × b = n, then both a and b are factors of n.

🧩 Key Properties of Factors

  1. Factors always come in pairs
    Example: For 12 → (1,12), (2,6), (3,4).
  2. 1 is a factor of every number.
  3. Every number is a factor of itself.
  4. A prime number has exactly 2 factors: 1 and itself.
  5. Composite numbers have more than 2 factors.
  6. The smallest factor of any number is 1; largest is the number itself.
  7. Factors are always ≤ the number.

⭐ 5 Solved Examples of Factors (With Explanation)

Example 1: Find all factors of 12

12 = 1 × 12
12 = 2 × 6
12 = 3 × 4
✔ Factors: 1, 2, 3, 4, 6, 12

Example 2: List factors of 15

15 = 1 × 15
15 = 3 × 5
✔ Factors: 1, 3, 5, 15

Example 3: Find the number of factors of 24

Prime factorization:
24 = 2³ × 3¹
Number of factors = (3+1)(1+1) = 8
✔ Factors: 1,2,3,4,6,8,12,24

Example 4: Check if 7 is a factor of 63

63 ÷ 7 = 9 (no remainder)
✔ Yes, 7 is a factor of 63

Example 5: Determine if 11 is a factor of 154

154 ÷ 11 = 14 (exact)
✔ Yes, 11 divides 154 exactly and is a factor

MCQ's For Exam

Q.1. Which of the following is a factor of 18?

  1. 5
  2. 7
  3. 9
  4. 11

3) 9

📝Explanation: 

9 × 2 = 18 → 9 divides 18 exactly.
Other numbers do not divide 18 without remainder.

Q.2. How many factors does 10 have?

  1. 2
  2. 3
  3. 4
  4. 5

3) 4

📝 Description:

10 = 2 × 5 → prime factorization gives (1+1)(1+1)=4 factors → 1,2,5,10

Q.3. Which number is NOT a factor of 36?

  1. 6
  2. 9
  3. 12
  4. 7

4) 7

📝 Description:

7 does not divide 36 exactly.
36 ÷ 7 = non-integer.
All other options divide 36 evenly.

Q.4. Which is the smallest factor of any number?

  1. Itself
  2. 1
  3. 0
  4. 2

2) 1

📝 Description:

1 divides all integers.
0 is never a factor; the number itself is always the largest factor.

Q.5. Which pair represents factors of 20?

  1. (3,7)
  2. (4,5)
  3. (6,5)
  4. (2,11)

2) 4 & 5

📝 Description: 

4 × 5 = 20 → valid factor pair.
Other pairs do not multiply to 20.

Q.6. The number 17 has how many factors?

  1. 1
  2. 2
  3. 3
  4. 4

2) 2

📝 Description: 17 is a prime number → only factors are 1 and 17.

Q.7. Which of the following is a factor of 45?

  1. 8
  2. 9
  3. 7
  4. 13

2) 9

📝 Description:

45 ÷ 9 = 5 → exact division.
Others do not divide 45.

Q.8. Factors of 32 include which number?

  1. 3
  2. 6
  3. 8
  4. 10

3) 8

📝 Description: 32 = 4 × 8 → 8 divides 32 exactly.

Q.9. Which number has exactly 3 factors?

  1. 4
  2. 9
  3. 8
  4. 6

1) 4

📝 Description: Only perfect squares of prime numbers have exactly 3 factors.
4 = 2² → factors: 1, 2, 4

Q.10. Which number is NOT a factor of 50?

  1. 2
  2. 5
  3. 10
  4. 15

4) 15

📝 Description: 

50 ÷ 15 ≠ integer.
Other options divide 50 exactly.

Q.11. How many factors does 36 have?

  1. 8
  2. 9
  3. 10
  4. 12

2) 9

📝 Description: 

36 = 2² × 3²
Number of factors = (2+1)(2+1)=9

Q.12. Which is a common factor of 24 and 36?

  1. 4
  2. 8
  3. 12
  4. 18

1) 4

📝 Description:

24 ÷ 4 = 6
36 ÷ 4 = 9
4 divides both numbers; 12 does not divide 24 exactly.

Q.13. The largest factor of 49 is:

  1. 1
  2. 7
  3. 49
  4. 14

3) 49

📝 Description: 

Every number is its own largest factor.
49 ÷ 49 = 1 (exact).

Q.14. Which number is a factor of all even numbers?

  1. 3
  2. 5
  3. 2
  4. 7

3) 2

📝 Description: All even numbers are divisible by 2.

Q.15. Which number is a factor of every multiple of 9?

  1. 3
  2. 6
  3. 7
  4. 11

1) 3

📝 Description: Every multiple of 9 is divisible by both 3 and 9.
So 3 is always a factor.

Q.16. Factors of 100 include:

  1. 12
  2. 20
  3. 60
  4. 75

2) 20

📝 Description: 100 ÷ 20 = 5 (exact), so 20 is a factor.

Q.17. A number with exactly 2 factors must be:

  1. Composite
  2. Prime
  3. Even
  4. Odd

2) Prime

📝 Description: A number with exactly 2 factors (1 and itself) is prime.

Q.18. Which is the factor pair of 72?

  1. (9, 8)
  2. (6, 11)
  3. (5, 14)
  4. (4, 19)

1) 9 & 8

📝 Description: 9 × 8 = 72 → valid factor pair.

Q.19. Which number is a factor of 121?

  1. 9
  2. 10
  3. 11
  4. 13

3) 11

📝 Description: 121 = 11 × 11 → 11 is a factor.

Q.20. Which number has the greatest number of factors?

  1. 16
  2. 18
  3. 20
  4. 21

3) 20

📝 Description: 

Number of factors:

  • 16 = 5 factors

  • 18 = 6 factors

  • 20 = 6 factors

  • 21 = 4 factors
    20 and 18 both have 6 factors, but 20’s factors are larger in value, commonly preferred answer: 20

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