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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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Expert · Level 3View options
Except only for the order of factors
Except only for the last digit of the number
Except only for even factors
By treating 1 as a prime factor
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(2^6\times3^2\times5\times7\times11)
(2^5\times3^3\times5\times7\times11)
(2^6\times3^2\times5^2\times7)
(20160\times11)
Expert · Level 3View options
7776
15552
23328
31104
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38482790400
19241395200
76965580800
12827596800
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2520
2880
3240
3600
Expert · Level 3View options
1940400
970200
1848000
2150400
Expert · Level 3View options
6
2
3
5
Expert · Level 3View options
30
15
60
42
Expert · Level 3View options
2450
1225
4900
7350
Expert · Level 3View options
(2\times3^3\times7^3\times13)
(2^2\times3^2\times7^3\times13)
(2\times3^3\times7^2\times13^2)
(42^3\times13)
Expert · Level 3View options
10
26
65
130
Expert · Level 3View options
(2^2\times3\times5\times7^2)
(2\times3^2\times5\times7)
(2^2\times3^2\times5^2\times7)
(2\times3\times5^2\times7^2)
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12
13
14
15
Expert · Level 3View options
10
11
12
13
Expert · Level 3View options
(2^9\times3^8)
(2^{12}\times3^{10})
(2^9\times3^8\times5\times7)
(2^3\times3^2)
Expert · Level 3View options
(2^{12}\times3^{10}\times5^4\times7^5)
(2^9\times3^8)
(2^{12}\times3^8\times5^4)
(2^9\times3^{10}\times7^5)
Expert · Level 3View options
1320
1200
1440
1680
Expert · Level 3View options
2016
1440
2160
2520
Expert · Level 3View options
3
4
5
6
Expert · Level 3View options
3
4
5
6
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22
23
24
25
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5
7
11
25
Expert · Level 3View options
They are co-prime
Their HCF is 13
Their common prime factor is 7
Their LCM is 1
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1
391
703
7429
Expert · Level 3View options
(2^{16})
(2^{15})
(4^8)
(16^4)
Question 1ExpertLevel 3
According to the Fundamental Theorem of Arithmetic, up to what extent is the prime factorisation of a number unique?
Correct answer: A
Step 1: The theorem gives certainty of prime factorisation for numbers greater than 1. Step 2: Prime factors and their powers remain fixed; only their order may change. Step 3: In the final answer, do not leave composite factors.
Which is the correct prime factorisation of 221760?
Correct answer: A
Step 1: Write (221760=20160\times11). Step 2: Since (20160=2^6\times3^2\times5\times7), the complete prime form is (2^6\times3^2\times5\times7\times11). Step 3: 20160 is composite, so do not keep it in the final answer.
If (a=2^8\times3^5\times5^2) and (b=2^5\times3^7\times7^3), what is the HCF of (a) and (b)?
Correct answer: A
Step 1: For HCF, take the smaller powers of common prime factors only. Step 2: The common factors are 2 and 3, with smaller powers (2^5) and (3^5). Step 3: (32\times243=7776), so the answer is 7776.
If (a=2^8\times3^5\times5^2) and (b=2^5\times3^7\times7^3), what is the LCM of (a) and (b)?
Correct answer: A
Step 1: For LCM, take the highest powers of all prime factors. Step 2: The highest powers are (2^8), (3^7), (5^2), and (7^3). Step 3: Their product is 38482790400, so that is the answer.
If the HCF of two numbers is 210 and their LCM is 9240, what is their product?
Correct answer: A
Step 1: The product of two numbers equals the product of their HCF and LCM. Step 2: (210\times9240=1940400). Step 3: Apply this formula directly only when exactly two numbers are involved.
What is the smallest positive number by which 21600 must be multiplied to get a perfect square?
Correct answer: A
Step 1: (21600=216\times100=2^5\times3^3\times5^2). Step 2: For a perfect square, all exponents must be even, but powers of 2 and 3 are odd. Step 3: Multiplying by (2\times3=6) makes all powers even.
By which smallest number should 52920 be divided to get a perfect square?
Correct answer: A
Step 1: (52920=2^3\times3^3\times5\times7^2). Step 2: For a perfect square, odd powers of 2, 3, and 5 must be reduced. Step 3: Dividing by (2\times3\times5=30) leaves (2^2\times3^2\times7^2).
What is the smallest number by which 30240 must be multiplied to get a perfect cube?
Correct answer: A
Step 1: (30240=2^5\times3^3\times5\times7). Step 2: For a perfect cube, exponents must be multiples of 3. Step 3: We need (2), (5^2), and (7^2), so the smallest multiplier is (2\times25\times49=2450).
Step 1: Write (500094=2\times250047). Step 2: (250047=3^3\times7^3\times13), so the full form is (2\times3^3\times7^3\times13). Step 3: Composite bases should not remain in final prime form.
If (N=2^{11}\times3^8\times5^7\times13^2), 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: Powers of 2 and 5 are odd, while the others are even. Step 3: Multiplying by (2\times5=10) makes all powers even.
If (N=2^{10}\times3^8\times5^5\times7), 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: We must make 10 to 12, 8 to 9, 5 to 6, and 1 to 3. Step 3: So the smallest multiplier is (2^2\times3\times5\times7^2).
If (a=2^7\times3^6\times5^2) and (b=2^5\times3^8\times7^3), 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 6 and in (b) is 8. Step 3: In (ab), the power of 3 is (6+8=14).
If (A=2^{12}\times3^8\times5^4) and (B=2^9\times3^{10}\times7^5), which is the HCF of (A) and (B)?
Correct answer: A
Step 1: HCF uses the smaller powers of common prime factors only. Step 2: The common factors are 2 and 3, with smaller powers (2^9) and (3^8). Step 3: So the correct form is (2^9\times3^8).
If (A=2^{12}\times3^8\times5^4) and (B=2^9\times3^{10}\times7^5), 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^{12}), (3^{10}), (5^4), and (7^5). Step 3: So the correct form is (2^{12}\times3^{10}\times5^4\times7^5).
The HCF of two numbers is 120 and their LCM is 9240. If one number is 840, what is the other number?
Correct answer: A
Step 1: Product of the two numbers is (120\times9240=1108800). Step 2: One number is 840, so the other is (1108800\div840=1320). Step 3: As a check, the HCF of 840 and 1320 is 120.
The HCF of two numbers is 144 and their LCM is 10080. If one number is 720, what is the other number?
Correct answer: A
Step 1: Product of the two numbers is (144\times10080=1451520). Step 2: The other number is (1451520\div720=2016). Step 3: To check, the HCF of 720 and 2016 is 144.
If (q=2^6\times3^b\times5^2\times7) and (q=1814400), what is the value of (b)?
Correct answer: B
Step 1: Write (1814400=18144\times100). Step 2: (18144=2^5\times3^4\times7) and (100=2^2\times5^2), so the actual form is (2^7\times3^4\times5^2\times7). Step 3: The power of 3 is (b=4).
If a number has prime factorisation (2^9\times3^7\times5^6\times17^2), how many prime factors are there if repetition is counted?
Correct answer: C
Step 1: To count with repetition, add the exponents. Step 2: (2^9) gives 9, (3^7) gives 7, (5^6) gives 6, and (17^2) gives 2 factors. Step 3: Total (9+7+6+2=24), so the answer is 24.
If a number has prime factorisation (2^{11}\times3^8\times5^3\times7^2\times13), how many distinct prime factors does it have?
Correct answer: A
Step 1: When counting distinct prime factors, exponents are not added. Step 2: The prime bases are 2, 3, 5, 7, and 13. Step 3: Therefore, the number of distinct prime factors is 5.
If the two numbers are (2^8\times3^4\times13) and (5^5\times7^3\times11), which statement about them is correct?
Correct answer: A
Step 1: The prime factors of the first number are 2, 3, and 13. Step 2: The prime factors of the second number are 5, 7, and 11. Step 3: There is no common prime factor, so they are co-prime.
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