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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. Six bells begin to toll together and toll, respectively, at intervals of 3, 4, 6, 7, 8 and 12 seconds. After how many seconds, will they toll together again?

  2. A and B are two prime numbers such that A > B and their LCM is 209. The value of A 2 - B is:

  3. Find the least number which when divided by 12, 18, 24 and 30 leaves 4 as remainder in each case, but when divided by 7 leaves no remainder.

  4. Calculate the HCF of \(\frac{12}{5}\) \(\frac{14}{15}\)  and  \(\frac{16}{17}\) .

  5. Three numbers are in the proportion of 3 : 8 : 15 and their LCM is 8280. What is their HCF?

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