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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.
If the HCF of two numbers is 78 and their LCM is 510510, what is the power of 13 in their product?
Correct answer: B
Step 1: The product is (78\times510510). Step 2: (78=2\times3\times13), and 510510 also has 13 to power 1. Step 3: Therefore, the power of 13 in the product is (1+1=2).
If (n=2^{10}\times3^8\times5^6), by which smallest number should (n) be divided to make it a perfect cube?
Correct answer: A
Step 1: In a perfect cube, every exponent must be a multiple of 3. Step 2: Reduce (2^{10}) to (2^9) by dividing by 2, and (3^8) to (3^6) by dividing by (3^2). Step 3: The smallest divisor is (2\times3^2).
Which option gives the number formed by (2^6\times3^4\times5\times7)?
Correct answer: A
Step 1: First calculate (2^6=64) and (3^4=81). Step 2: (64\times81\times5\times7=181440). Step 3: To get the number from prime factorisation, multiply all factors.
If (a=2^7\times3^3\times5) and (b=2^4\times3^6\times5^2), the product of their HCF and LCM will be equal to what?
Correct answer: A
Step 1: For two numbers, HCF (\times) LCM equals the product of the two numbers. Step 2: In prime powers, the smaller and higher exponents together give the total exponent. Step 3: Therefore, the answer is (ab).
If (x=2^5\times3^6\times5^4) and (y=2^7\times3^3\times5^5), how many prime factors will (xy) have if repetition is counted?
Correct answer: C
Step 1: In (xy), exponents of the same bases are added. Step 2: Powers become (2^{12}), (3^9), and (5^9). Step 3: Counting with repetition gives (12+9+9=30).
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.
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