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Question

Find the LCM of 8, 12, and 20.

The correct answer is
120

Finding LCM of 8, 12, and 20

The Least Common Multiple (LCM) is the smallest positive integer that is divisible by each of the given numbers.

Prime Factorization Method

We can find the LCM using the prime factorization method:

  • Step 1: Find the prime factorization of each number.
    • $8 = 2 \times 2 \times 2 = 2^3$
    • $12 = 2 \times 2 \times 3 = 2^2 \times 3^1$
    • $20 = 2 \times 2 \times 5 = 2^2 \times 5^1$
  • Step 2: Identify all the unique prime factors present in any of the factorizations.

    The unique prime factors are 2, 3, and 5.

  • Step 3: Take the highest power of each unique prime factor.
    • Highest power of 2 is $2^3$.
    • Highest power of 3 is $3^1$.
    • Highest power of 5 is $5^1$.
  • Step 4: Multiply these highest powers together to get the LCM.

    LCM = $2^3 \times 3^1 \times 5^1 = 8 \times 3 \times 5 = 120$.

Therefore, the LCM of 8, 12, and 20 is 120.

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Important Questions from LCM and HCF

  1. The greatest three-digit number which is divisible by 14, 28, and 42 is:

  2. What is the greatest number that will divide 209 and 347 leaving remainder 5 and 7 respectively?

  3. A number is three times another number and their HCF is 8. What is the sum of the squares of the numbers?

  4. The HCF of 2091, 3485 and 4879 is x. The sum of the digits of x is:

  5. If three numbers are in ratio of 3 : 5 : 7 and their LCM is 2415, what is the difference between the second number and the first number?

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