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Question

The number 311 311 311 311 311 311 311 is ______

The correct answer is
neither divisible by 3 nor by 11

To determine whether the number \( 311311311311311311311 \) is divisible by 3 or 11, we need to apply the divisibility rules for these numbers.

Divisibility by 3

A number is divisible by 3 if the sum of its digits is divisible by 3.

  1. Identify the digits of the number: In \( 311311311311311311311 \), the digits are repeated sequences of 3, 1, and 1.
  2. Count and sum the digits:
    • 3 is repeated 7 times.
    • 1 is repeated 14 times.
    • Sum of all digits = \( 7 \times 3 + 14 \times 1 = 21 + 14 = 35 \).
  3. Check divisibility: 35 is not divisible by 3 (since \( 35 \div 3 \) leaves a remainder).

Thus, the number is not divisible by 3.

Divisibility by 11

A number is divisible by 11 if the difference between the sum of the digits at odd positions and the sum of the digits at even positions is either 0 or divisible by 11.

  1. Split the number into odd and even positions:
    • Odd positions: 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3
    • Even positions: 1, 3, 1, 3, 1, 3, 1, 3, 1, 3
  2. Calculate the sum of odd and even positions:
    • Sum of odd-positioned digits = \( 22 \) (sum calculated as \( 3+1+3+1+...+3 \)).
    • Sum of even-positioned digits = \( 13 \) (sum calculated as \( 1+3+1+3+...+3 \)).
    • Difference = \( 22 - 13 = 9 \).
  3. Check divisibility: 9 is not divisible by 11.

Thus, the number is not divisible by 11.

Conclusion

Since the number \( 311311311311311311311 \) is neither divisible by 3 nor by 11, the correct answer is:

Option: Neither divisible by 3 nor by 11.

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Important Questions from Divisibility and Remainder

  1. If all positive divisors of 132 are arranged in descending order, then what digit will be at unit place of first divisor ?

  2. If 3 2019 is divided by 10, then what is the remainder?

  3. The number 3798125P369 is divisible by 7. What is the value of the digit P?

  4. Consider all 3-digit numbers (without repetition of digits) obtained using three non-zero digits which are multiples of 3. Let S be their sum.

    Which of the following is/are correct?

    1. S is always divisible by 74.

    2. S is always divisible by 9.

    select the correct answer using the code given below:

  5. How many 3-digit natural numbers (without repetition of digits) are there such that each digit is odd and the number is divisible by 5?

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