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In this Class 10 Mathematics topic from Real Numbers, students learn to find the HCF and LCM of two or more numbers through prime factorisation. They break each number into prime factors, compare the resulting powers, and select the appropriate common factors: the lowest powers for HCF and the highest powers for LCM. The topic also develops accuracy in writing factor trees, simplifies comparison between methods, and helps students apply these concepts to numerical and everyday problem-solving situations.
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Medium · Level 5 · real-numbers,fundamental-theorem-of-arithmetic,hcf-lcm,number-system,grade-10View options
If the product of two numbers is 3780 and their LCM is 315, what is their HCF?
Correct answer: B
For two positive integers, the relation is: product = HCF \(\times\) LCM. Therefore, HCF \(=3780\div315=12\). Hence, option B is correct. Exam tip: To find the HCF, divide the product by the LCM and verify that the quotient is a whole number.
What is the HCF of (18) and (24) using prime factorisation?
Correct answer: B
Step 1: (18=2\times3^2) and (24=2^3\times3). Step 2: Taking the smaller powers of common prime factors gives (2\times3=6). Step 3: For HCF, take only common prime factors.
What is the LCM of (18) and (24) using prime factorisation?
Correct answer: C
Step 1: (18=2\times3^2) and (24=2^3\times3). Step 2: Taking the highest powers of all prime factors gives (2^3\times3^2=72). Step 3: For LCM, include both common and uncommon prime factors.
Step 1: (40=2^3\times5) and (60=2^2\times3\times5). Step 2: The common factors with smaller powers are (2^2) and (5). Step 3: (2^2\times5=20), so the HCF is (20).
Step 1: (40=2^3\times5) and (60=2^2\times3\times5). Step 2: Use the highest powers (2^3), (3), and (5). Step 3: (2^3\times3\times5=120), so the LCM is (120).
Step 1: (45=3^2\times5) and (75=3\times5^2). Step 2: Take the smaller powers of the common prime factors (3) and (5). Step 3: (3\times5=15), so the HCF is (15).
Step 1: (32=2^5) and (48=2^4\times3). Step 2: The only common prime factor is (2), and the smaller power is (2^4). Step 3: (2^4=16), so the HCF is (16).
Step 1: (72=2^3\times3^2) and (90=2\times3^2\times5). Step 2: The smaller powers of common factors are (2) and (3^2). Step 3: (2\times9=18), so the HCF is (18).
Step 1: (72=2^3\times3^2) and (90=2\times3^2\times5). Step 2: The highest powers are (2^3), (3^2), and (5). Step 3: (8\times9\times5=360), so the LCM is (360).
Step 1: (12=2^2\times3), (18=2\times3^2), and (30=2\times3\times5). Step 2: The common prime factors in all three numbers are (2) and (3). Step 3: (2\times3=6), so the HCF is (6).
Step 1: (12=2^2\times3), (18=2\times3^2), and (30=2\times3\times5). Step 2: Use the highest powers (2^2), (3^2), and (5). Step 3: (4\times9\times5=180), so the LCM is (180).
Step 1: (16=2^4), (24=2^3\times3), and (40=2^3\times5). Step 2: The common prime factor is (2), and the smallest power is (2^3). Step 3: (2^3=8), so the HCF is (8).
Step 1: (16=2^4), (24=2^3\times3), and (40=2^3\times5). Step 2: Take the highest powers (2^4), (3), and (5). Step 3: (16\times3\times5=240), so the LCM is (240).
If (a=2^2\times3\times5) and (b=2\times3^2\times5), what is the HCF of (a) and (b)?
Correct answer: B
Step 1: The common prime factors are (2), (3), and (5). Step 2: Their smaller powers are (2), (3), and (5). Step 3: (2\times3\times5=30), so the HCF is (30).
If (a=2^2\times3\times5) and (b=2\times3^2\times5), what is the LCM of (a) and (b)?
Correct answer: C
Step 1: For LCM, take the highest powers of all prime factors. Step 2: The highest powers are (2^2), (3^2), and (5). Step 3: (4\times9\times5=180), so the LCM is (180).
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