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Question

If 9A7B is divisible by 55, find A + B.

The correct answer is
5

To solve the problem of finding the sum A + B where the number \(9A7B\) is divisible by 55, we need to understand the divisibility rule for 55. A number is divisible by 55 if it is divisible by both 5 and 11.

Divisibility by 5: A number is divisible by 5 if its last digit is 0 or 5. Therefore, \(B\) should be 0 or 5. Let's consider \(B = 5\) as this satisfies divisibility by 5.

Divisibility by 11: A number is divisible by 11 if the difference between the sum of its digits at odd positions and the sum of its digits at even positions is a multiple of 11.

For the number 9A7B:

  • Odd-positioned digits: 9 and 7
  • Even-positioned digits: A and 5

To satisfy the equation, we need:

\(11 - A = 0 \Rightarrow A = 11\)

However, \(A\) must be a singular digit. Adjust \(B\) so \(11 - A = \text{multiple of } 11\), such that it keeps within a valid digit scope.

Using \(B = 5\) previously determined:

For \(A = 0\), the expression becomes: \(16 - (0 + 5) = 11\), satisfying the divisibility rule for 11.\)

Thus, \(A = 0\) and \(B = 5\).

Therefore, \(A + B = 0 + 5 = 5\).

Conclusion: The sum A + B is \(5\).

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Important Questions from Divisibility and Remainder

  1. If a five digit number 247xy is divisible by 3, 7 and 11, then what is the value of (2y - 8x)?

  2. If the seven-digit number 94x29y6 is divisible by 72, then what is the value of (2x + 3y) for x ≠ y ?

  3. Find the greatest value of b so that 30a68b (a > b) is divisible by 11.

  4. What is the remainder when the product of 335, 608 and 853 is divided by 13?

  5. What is the least square number which is exactly divisible by 2, 3, 10, 18 and 20?
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