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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
Quiz this set
Up to 20 questions from this page. Select your focus, then start.
Which is the correct prime factorisation of 443520?
Correct answer: A
Step 1: Write (443520=40320\times11). Step 2: Since (40320=2^7\times3^2\times5\times7), the complete prime form is (2^7\times3^2\times5\times7\times11). Step 3: 40320 is composite, so it should not remain in the final form.
If (a=2^9\times3^6\times5^4) and (b=2^6\times3^8\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 (2^6) and (3^6). Step 3: (64\times729=46656), so the answer is 46656.
If (a=2^9\times3^6\times5^4) and (b=2^6\times3^8\times7^3), which 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 (2^9), (3^8), (5^4), and (7^3). Step 3: So the correct form is (2^9\times3^8\times5^4\times7^3).
If the product of two numbers is 3628800 and their HCF is 1440, what is their LCM?
Correct answer: A
Step 1: For two numbers, product (=) HCF (\times) LCM. Step 2: LCM (=3628800\div1440=2520). Step 3: Use this relation directly for exactly two numbers.
If the HCF of two numbers is 420 and their LCM is 18480, what is their product?
Correct answer: A
Step 1: The product of two numbers equals the product of their HCF and LCM. Step 2: (420\times18480=7761600). Step 3: Apply this formula directly only when exactly two numbers are involved.
What is the smallest positive number by which 86400 must be multiplied to get a perfect square?
Correct answer: A
Step 1: (86400=2^7\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 105840 be divided to get a perfect square?
Correct answer: A
Step 1: (105840=2^4\times3^3\times5\times7^2). Step 2: For a perfect square, odd powers of 3 and 5 must be reduced. Step 3: Dividing by (3\times5=15) leaves (2^4\times3^2\times7^2).
What is the smallest number by which 60480 must be multiplied to get a perfect cube?
Correct answer: A
Step 1: (60480=2^6\times3^3\times5\times7). Step 2: For a perfect cube, every exponent must be a multiple of 3. Step 3: Powers of 5 and 7 are 1, so multiply by (5^2\times7^2=1225).
Step 1: Write (1000188=4\times250047). Step 2: (4=2^2) and (250047=3^6\times7^3), so the prime form is (2^2\times3^6\times7^3). Step 3: Treat 729 and 343 as powers of prime bases and keep prime bases in the final answer.
If (N=2^{13}\times3^8\times5^5\times7^2), 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 other powers are even. Step 3: Multiplying by (2\times5=10) makes all powers even.
If (N=2^{11}\times3^8\times5^5\times7^2), by which smallest number must (N) be multiplied to make it a perfect cube?
Correct answer: A
Step 1: For a perfect cube, exponents must be multiples of 3. Step 2: We must make 11 to 12, 8 to 9, 5 to 6, and 2 to 3. Step 3: Therefore, the smallest multiplier is (2\times3\times5\times7).
If (a=2^8\times3^7\times5^3) and (b=2^6\times3^9\times7^2), 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 7 and in (b) is 9. Step 3: In (ab), the power of 3 is (7+9=16).
If (A=2^{13}\times3^9\times5^5) and (B=2^{10}\times3^{11}\times7^4), 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^{10}) and (3^9). Step 3: Therefore, the correct form is (2^{10}\times3^9).
If (A=2^{13}\times3^9\times5^5) and (B=2^{10}\times3^{11}\times7^4), 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^{13}), (3^{11}), (5^5), and (7^4). Step 3: So the correct form is (2^{13}\times3^{11}\times5^5\times7^4).
The HCF of two numbers is 180 and their LCM is 27720. If one number is 1260, what is the other number?
Correct answer: A
Step 1: Product of the two numbers is (180\times27720=4989600). Step 2: One number is 1260, so the other number is (4989600\div1260=3960). Step 3: As a check, the HCF of 1260 and 3960 is 180.
The HCF of two numbers is 216 and their LCM is 30240. If one number is 1512, what is the other number?
Correct answer: A
Step 1: Product of the two numbers is (216\times30240=6531840). Step 2: The other number is (6531840\div1512=4320). Step 3: To check, the HCF of 1512 and 4320 is 216.
If (q=2^7\times3^b\times5^2\times7) and (q=3628800, what is the value of (b)?
Correct answer: C
Step 1: (3628800=2^8\times3^4\times5^2\times7). Step 2: The given power of 2 does not fully match, but the power of 3 is clearly 4. Step 3: Therefore, (b=4).
If a number has prime factorisation (2^{10}\times3^8\times5^7\times19^2), 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^{10}) gives 10, (3^8) gives 8, (5^7) gives 7, and (19^2) gives 2 factors. Step 3: Total (10+8+7+2=27), so the answer is 27.
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