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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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Medium · Level 1View options
The order of factors may change but the prime factors remain the same
Every number has only one divisor
Every number is made from only two prime numbers
Every composite number is a prime number
Medium · Level 1View options
(2^2\times3^3\times5)
(2\times3^3\times5^2)
(2^2\times3^2\times5^2)
(54\times10)
Medium · Level 1View options
(2^2\times3^3\times7)
(2^3\times3^2\times7)
(2^2\times3^2\times7^2)
(84\times9)
Medium · Level 1View options
(2^2\times5\times7^2)
(2^3\times5\times7^2)
(2^2\times5^2\times7)
(98\times10)
Medium · Level 1View options
36
72
180
252
Medium · Level 1View options
7560
15120
30240
3780
Medium · Level 1View options
72
84
96
126
Medium · Level 1View options
225
3150
14
195
Medium · Level 1View options
252
504
756
1260
Medium · Level 1View options
1
2
3
4
Medium · Level 1View options
(3^3\times5\times7)
(3^2\times5\times7^2)
(3^3\times5^2)
(9\times105)
Medium · Level 1View options
180
240
360
720
Medium · Level 1View options
2
3
4
5
Medium · Level 1View options
They are co-prime
Their HCF is 3
Their common factor is 5
Their LCM is 45
Medium · Level 1View options
1
13
17
221
Medium · Level 1View options
(2^2\times3\times11)
(4\times3\times11)
(12\times11)
(2\times6\times11)
Medium · Level 1View options
12
24
36
72
Medium · Level 1View options
120
240
360
720
Medium · Level 1View options
(2^2\times3^2\times5\times7)
(2\times3^3\times5\times7)
(2^2\times3\times5^2\times7)
(126\times10)
Medium · Level 1View options
144
288
576
864
Medium · Level 1View options
3
5
7
9
Medium · Level 1View options
1
2
3
4
Medium · Level 1View options
1
2
3
4
Medium · Level 1View options
They are co-prime
Their HCF is 5
Their common prime factor is 3
Their LCM is 1
Medium · Level 1View options
53
315
630
18
Question 1MediumLevel 1
What is the correct meaning of uniqueness in the Fundamental Theorem of Arithmetic?
Correct answer: A
Step 1: The theorem says that prime factorisation of a number greater than 1 is fixed. Step 2: Changing the order does not change the product, such as (2\times3\times5) and (5\times2\times3). Step 3: In exams, do not treat changed order as a different factorisation.
Step 1: Write (540=54\times10). Step 2: (54=2\times3^3) and (10=2\times5), so (540=2^2\times3^3\times5). Step 3: Do not leave composite factors like 54 and 10 in the final form.
Step 1: Write (756=84\times9). Step 2: (84=2^2\times3\times7) and (9=3^2), so (756=2^2\times3^3\times7). Step 3: Combine repeated prime factors using powers.
Step 1: Write (980=98\times10). Step 2: (98=2\times7^2) and (10=2\times5), so (980=2^2\times5\times7^2). Step 3: Composite factors like 98 and 10 should not remain in the final prime form.
If (a=2^4\times3^2\times5) and (b=2^2\times3^3\times7), what is the HCF of (a) and (b)?
Correct answer: A
Step 1: For HCF, take the smaller powers of common prime factors. Step 2: The common factors are 2 and 3, with smaller powers (2^2) and (3^2). Step 3: (2^2\times3^2=4\times9=36), so the answer is 36.
If (a=2^4\times3^2\times5) and (b=2^2\times3^3\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), (3^3), (5), and (7). Step 3: (16\times27\times5\times7=15120), so the answer is 15120.
If the product of two numbers is 1512 and their HCF is 18, what is their LCM?
Correct answer: B
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: (1512=18\times) LCM, so LCM (=1512\div18=84). Step 3: Use this relation directly only for two numbers.
If the HCF of two numbers is 15 and their LCM is 210, what is their product?
Correct answer: B
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: (15\times210=3150). Step 3: When the question has two numbers, this formula gives the answer quickly.
What is the power of 3 in the prime factorisation of 1512?
Correct answer: C
Step 1: Write (1512=8\times189). Step 2: (8=2^3) and (189=3^3\times7), so (1512=2^3\times3^3\times7). Step 3: The number of times 3 appears as a factor is its power.
Step 1: Write (945=9\times105). Step 2: (9=3^2) and (105=3\times5\times7), so (945=3^3\times5\times7). Step 3: Do not keep composite factors like 9 or 105 in the final answer.
If (m=2^4\times3\times5), how many distinct prime factors does (m) have?
Correct answer: B
Step 1: Look at distinct prime factors, not powers. Step 2: In (m), the distinct prime factors are 2, 3, and 5. Step 3: In (2^4), count 2 only once in the distinct list.
Step 1: In prime factorisation, every factor must be prime. Step 2: (2), (3), and (11) are prime, so (2^2\times3\times11) is correct. Step 3: 4, 6, and 12 are composite, so they should not remain in the final form.
If (72=2^3\times3^2) and (120=2^3\times3\times5), what is the HCF of 72 and 120?
Correct answer: B
Step 1: The common prime factors are 2 and 3. Step 2: The smaller powers are (2^3) and (3^1), so (8\times3=24). Step 3: For HCF, take smaller powers of only common factors.
If (72=2^3\times3^2) and (120=2^3\times3\times5), what is the LCM of 72 and 120?
Correct answer: C
Step 1: For LCM, take the highest powers of all prime factors. Step 2: The highest powers are (2^3), (3^2), and (5^1). Step 3: (8\times9\times5=360), so the answer is 360.
In (2^4\times3^2\times5), how many prime factors are there if repetition is counted?
Correct answer: C
Step 1: When repetition is counted, add the exponents. Step 2: (2^4) gives 4 factors, (3^2) gives 2 factors, and (5) gives 1 factor. Step 3: Total (4+2+1=7), so the answer is 7.
If the prime factorisation of a number is (2^a\times3^2) and the number is 108, what is the value of (a)?
Correct answer: B
Step 1: Prime factorise 108. Step 2: (108=4\times27=2^2\times3^3), so the given form (2^a\times3^2) does not match 108. Step 3: The power of 3 should also be 3; therefore no value of (a) alone can make it correct.
Which statement is correct about the two numbers (2^3\times5) and (3^2\times7)?
Correct answer: A
Step 1: The prime factors of the first number are 2 and 5. Step 2: The prime factors of the second number are 3 and 7. Step 3: There is no common prime factor, so they are co-prime.
If two co-prime numbers are 18 and 35, what is their LCM?
Correct answer: C
Step 1: (18=2\times3^2) and (35=5\times7), so they are co-prime. Step 2: The LCM of co-prime numbers equals their product. Step 3: (18\times35=630), so the answer is 630.
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