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Question

Find the least number which when divided by 4, 6, 8, 10 and 12 leaves the remainder 3 in all cases.

The correct answer is
123

The problem asks for the least number that leaves a remainder of 3 when divided by 4, 6, 8, 10, and 12.

Finding the Least Common Multiple (LCM)

To find the least number satisfying the condition, we first need to find the Least Common Multiple (LCM) of the divisors: 4, 6, 8, 10, and 12.

  1. Prime Factorization: Find the prime factors of each number.
    • $4 = 2^2$
    • $6 = 2 \times 3$
    • $8 = 2^3$
    • $10 = 2 \times 5$
    • $12 = 2^2 \times 3$
  2. Calculate LCM: The LCM is found by taking the highest power of each prime factor present in any of the numbers.
    • The prime factors involved are 2, 3, and 5.
    • Highest power of 2 is $2^3$.
    • Highest power of 3 is $3^1$.
    • Highest power of 5 is $5^1$.

    Therefore, $\text{LCM}(4, 6, 8, 10, 12) = 2^3 \times 3^1 \times 5^1 = 8 \times 3 \times 5 = 120$.

Calculating the Final Number

The problem states that the number leaves a remainder of 3 in all cases. This means the required number is 3 more than the LCM of the divisors.

Least Number = LCM + Remainder

Least Number = $120 + 3 = 123$.

Verification

Let's check if 123 leaves a remainder of 3:

  • $123 \div 4 = 30$ remainder $3$ ($123 = 4 \times 30 + 3$)
  • $123 \div 6 = 20$ remainder $3$ ($123 = 6 \times 20 + 3$)
  • $123 \div 8 = 15$ remainder $3$ ($123 = 8 \times 15 + 3$)
  • $123 \div 10 = 12$ remainder $3$ ($123 = 10 \times 12 + 3$)
  • $123 \div 12 = 10$ remainder $3$ ($123 = 12 \times 10 + 3$)

The condition holds true for the number 123.

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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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