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In this Class 10 Mathematics topic from the chapter Real Numbers, students learn that every integer greater than 1 can be expressed as a product of prime numbers, and that this prime factorisation is unique apart from the order of the factors. They practise finding prime factors and use the theorem to understand and determine the HCF and LCM of numbers. The topic builds clear reasoning about the structure of whole numbers and supports later work with divisibility and number relationships.
TOPIC PRACTICE
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Hard · Level 1View options
They will differ only in order
Both will always be wrong
The number must be prime
The number will have no factorisation
Hard · Level 1View options
(2^3\times3^2\times5\times7\times11)
(2^2\times3^3\times5\times7\times11)
(2^3\times3^2\times5^2\times7)
(2520\times11)
Hard · Level 1View options
108
216
432
972
Hard · Level 1View options
340200
680400
170100
226800
Hard · Level 1View options
720
840
960
1080
Hard · Level 1View options
56700
56070
28000
1305
Hard · Level 1View options
2
3
5
10
Hard · Level 1View options
5
7
35
14
Hard · Level 1View options
10
20
30
45
Hard · Level 1View options
(3^3\times7^3)
(3^2\times7^4)
(3^4\times7^2)
(21^3)
Hard · Level 1View options
14
21
35
42
Hard · Level 1View options
(2^2\times3\times5)
(2\times3\times5)
(2^2\times3^2\times5)
(2\times3^2\times5^2)
Hard · Level 1View options
4
5
6
8
Hard · Level 1View options
4
5
6
8
Hard · Level 1View options
(2^5\times3^4)
(2^8\times3^6)
(2^5\times3^4\times5\times7)
(2^3\times3^2)
Hard · Level 1View options
(2^8\times3^6\times5^2\times7)
(2^5\times3^4)
(2^8\times3^4\times5^2)
(2^5\times3^6\times7)
Hard · Level 1View options
108
120
126
144
Hard · Level 1View options
168
180
192
210
Hard · Level 1View options
2
3
4
5
Hard · Level 1View options
1
2
3
4
Hard · Level 1View options
7
8
9
10
Hard · Level 1View options
3
6
11
12
Hard · Level 1View options
They are co-prime
Their HCF is 5
Their common prime factor is 3
Their LCM is 1
Hard · Level 1View options
1
77
143
1001
Hard · Level 1View options
(2^{12})
(2^{10})
(4^6)
(16^3)
Question 1HardLevel 1
According to the Fundamental Theorem of Arithmetic, if two different prime factorisations of a number seem to appear, what is the correct conclusion?
Correct answer: A
Step 1: The Fundamental Theorem of Arithmetic states uniqueness of prime factorisation. Step 2: The order of prime factors may change, but the prime factors themselves do not change. Step 3: In exams, do not treat a change of order as a different factorisation.
Step 1: Write (27720=2520\times11). Step 2: Since (2520=2^3\times3^2\times5\times7), the full factorisation is (2^3\times3^2\times5\times7\times11). Step 3: Do not leave a composite factor like 2520 in the final answer.
If (a=2^4\times3^3\times5^2) and (b=2^2\times3^5\times7), what is the HCF of (a) and (b)?
Correct answer: A
Step 1: For HCF, take the smaller powers of only the common prime factors. Step 2: The common prime factors are 2 and 3, with smaller powers (2^2) and (3^3). Step 3: (2^2\times3^3=4\times27=108), so the answer is 108.
If (a=2^4\times3^3\times5^2) and (b=2^2\times3^5\times7), what is the LCM of (a) and (b)?
Correct answer: B
Step 1: For LCM, take the highest powers of all prime factors. Step 2: The highest powers are (2^4), (3^5), (5^2), and (7). Step 3: (16\times243\times25\times7=680400), so the answer is 680400.
If the product of two numbers is 60480 and their HCF is 72, what is their LCM?
Correct answer: B
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: Therefore, LCM (=60480\div72=840). Step 3: Use this relation directly only for two numbers.
If the HCF of two numbers is 45 and their LCM is 1260, what is their product?
Correct answer: A
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: (45\times1260=56700). Step 3: In such questions, first notice that exactly two numbers are involved.
What is the smallest positive number by which 1800 must be multiplied to get a perfect square?
Correct answer: A
Step 1: (1800=18\times100=2^3\times3^2\times5^2). Step 2: For a perfect square, all exponents must be even, but the exponent of 2 is 3. Step 3: Multiplying by 2 makes it 4, so the smallest number is 2.
By which smallest number should 8820 be divided to get a perfect square?
Correct answer: C
Step 1: (8820=2^2\times3^2\times5\times7^2). Step 2: For a perfect square, all exponents must be even, but the exponent of 5 is 1. Step 3: Dividing by 5 makes all remaining exponents even, so the smallest number is 5.
What is the smallest number by which 5400 must be multiplied to get a perfect cube?
Correct answer: A
Step 1: (5400=54\times100=2^3\times3^3\times5^2). Step 2: For a perfect cube, each prime exponent must be a multiple of 3. Step 3: The exponent of 5 is 2, so one more 5 is needed; the smallest number is 5.
Step 1: Recognise (9261=21^3). Step 2: Since (21=3\times7), (21^3=3^3\times7^3). Step 3: (21^3) gives the value, but 21 is not prime, so write the final prime form separately.
If (N=2^5\times3^4\times5^2\times7), by which smallest number must (N) be multiplied to make it a perfect square?
Correct answer: A
Step 1: For a perfect square, every exponent must be even. Step 2: The exponents of (2^5) and (7^1) are odd, while the others are even. Step 3: Multiplying by (2\times7=14) makes all exponents even.
If (N=2^4\times3^5\times5^2), by which smallest number must (N) be multiplied to make it a perfect cube?
Correct answer: A
Step 1: For a perfect cube, every exponent must be a multiple of 3. Step 2: To make powers (4,5,2) into (6,6,3), we need (2^2), (3), and (5). Step 3: So the smallest multiplier is (2^2\times3\times5).
If (a=2^3\times3^2\times5) and (b=2^2\times3^4\times7), what will be the power of 3 in (ab)?
Correct answer: C
Step 1: In multiplication, exponents of the same prime base are added. Step 2: The power of 3 in (a) is 2 and in (b) is 4. Step 3: In (ab), the power of 3 will be (2+4=6).
If (A=2^8\times3^4\times5^2) and (B=2^5\times3^6\times7), what is the HCF of (A) and (B)?
Correct answer: A
Step 1: HCF uses only common prime factors. Step 2: The common factors are 2 and 3; the smaller powers are (2^5) and (3^4). Step 3: Therefore, the HCF is (2^5\times3^4).
If (A=2^8\times3^4\times5^2) and (B=2^5\times3^6\times7), which is the LCM of (A) and (B)?
Correct answer: A
Step 1: LCM uses the highest powers of all prime factors. Step 2: The highest powers are (2^8), (3^6), (5^2), and (7). Step 3: So the correct form is (2^8\times3^6\times5^2\times7).
The HCF of two numbers is 18 and their LCM is 540. If one number is 90, what is the other number?
Correct answer: A
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: Product of the two numbers is (18\times540=9720). Step 3: The other number is (9720\div90=108).
The HCF of two numbers is 24 and their LCM is 840. If one number is 120, what is the other number?
Correct answer: A
Step 1: Product of the two numbers is (24\times840=20160). Step 2: One number is 120, so the other is (20160\div120=168). Step 3: You can check the answer by confirming that HCF of 120 and 168 is 24.
If a number has prime factorisation (2^4\times3^3\times5^2), how many prime factors are there if repetition is counted?
Correct answer: C
Step 1: To count with repetition, add the exponents. Step 2: (2^4) gives 4, (3^3) gives 3, and (5^2) gives 2 factors. Step 3: Total (4+3+2=9), so the answer is 9.
If a number has prime factorisation (2^6\times3^2\times7^3), how many distinct prime factors does it have?
Correct answer: A
Step 1: When counting distinct prime factors, do not add exponents. Step 2: The prime factors here are 2, 3, and 7. Step 3: Therefore, the number of distinct prime factors is 3.
If the two numbers are (2^5\times3) and (5^2\times7), which statement is correct about them?
Correct answer: A
Step 1: The first number has prime factors 2 and 3. Step 2: The second number has prime factors 5 and 7. Step 3: There is no common prime factor, so they are co-prime.
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