State Exam — Quantitative Aptitude — HCF and LCM
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Q.1 Easy HCF and LCM
Find the HCF of 48 and 64.
A8
B16
C32
D24
Correct Answer:  B. 16
Explanation:

Using prime factorization: 48 = 2⁴ × 3, 64 = 2⁶. HCF = 2⁴ = 16 (taking lowest powers of common prime factors).

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Q.2 Easy HCF and LCM
What is the LCM of 12 and 18?
A36
B24
C54
D72
Correct Answer:  A. 36
Explanation:

Prime factorization: 12 = 2² × 3, 18 = 2 × 3². LCM = 2² × 3² = 4 × 9 = 36 (taking highest powers of all prime factors).

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Q.3 Easy HCF and LCM
Find the HCF of 56 and 72.
A4
B8
C12
D16
Correct Answer:  B. 8
Explanation:

This question asks us to find the Highest Common Factor (HCF) of two numbers using prime factorization or the Euclidean algorithm.

Step 1: Prime factorization of 56

Express 56 as a product of prime numbers.

\[56 = 2 \times 2 \times 2 \times 7 = 2^3 \times 7\]
Step 2: Prime factorization of 72

Express 72 as a product of prime numbers.

\[72 = 2 \times 2 \times 2 \times 3 \times 3 = 2^3 \times 3^2\]
Step 3: Find the HCF

The HCF is the product of common prime factors with their lowest powers.

\[\text{HCF} = 2^3 = 8\]

The HCF of 56 and 72 is 8, making the correct answer (B).

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Q.4 Easy HCF and LCM
The LCM of 15 and 25 is:
A75
B150
C225
D300
Correct Answer:  A. 75
Explanation:

This question asks us to find the Least Common Multiple (LCM) of two numbers using prime factorization.

Step 1: Find prime factorization of 15

Break 15 into its prime factors.

\[15 = 3 \times 5\]
Step 2: Find prime factorization of 25

Break 25 into its prime factors.

\[25 = 5 \times 5 = 5^2\]
Step 3: Calculate LCM using highest powers of all prime factors

The LCM is found by taking the highest power of each prime that appears in either factorization: 3¹ and 5².

\[\text{LCM} = 3^1 \times 5^2 = 3 \times 25 = 75\]

The LCM of 15 and 25 is 75.

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Q.5 Easy HCF and LCM
The product of two numbers is 2160 and their HCF is 12. Find their LCM.
A180
B240
C300
D360
Correct Answer:  A. 180
Explanation:

Using the formula: HCF × LCM = Product of two numbers.

Therefore, 12 × LCM = 2160, so LCM = 2160 ÷ 12 = 180.

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Q.6 Easy HCF and LCM
What is the HCF of 18 and 27?
A6
B9
C12
D18
Correct Answer:  B. 9
Explanation:

Factors of 18: 1, 2, 3, 6, 9, 18.

Factors of 27: 1, 3, 9, 27.

Common factors: 1, 3, 9.

Highest common factor = 9.

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Q.7 Easy HCF and LCM
Find the LCM of 20 and 30.
A30
B60
C90
D120
Correct Answer:  B. 60
Explanation:

20 = 2² × 5, 30 = 2 × 3 × 5. LCM = 2² × 3 × 5 = 4 × 3 × 5 = 60.

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Q.8 Easy HCF and LCM
The LCM of two co-prime numbers is 221. What is the product of the numbers?
A110
B221
C442
D221
Correct Answer:  B. 221
Explanation:

For co-prime numbers, HCF = 1.

Using HCF × LCM = Product: 1 × 221 = Product.

Therefore, product = 221.

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Q.9 Easy HCF and LCM
Find the smallest number that is divisible by 12, 15, and 20.
A60
B120
C180
D240
Correct Answer:  A. 60
Explanation:

12 = 2² × 3, 15 = 3 × 5, 20 = 2² × 5. LCM = 2² × 3 × 5 = 60.

This is the smallest number divisible by all three.

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Q.10 Easy HCF and LCM
The HCF of two consecutive even numbers is:
A1
B2
C4
DThe product of the numbers
Correct Answer:  B. 2
Explanation:

Consecutive even numbers differ by 2.

Examples: HCF(2,4)=2, HCF(6,8)=2, HCF(10,12)=2.

The HCF is always 2.

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