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      Question

      If a nine-digit number 89563x87y is divisible by 72,

      then the value of √ (5x -4y) will be ∢
      A 17 Correct Answer Incorrect Answer
      B 12 Correct Answer Incorrect Answer
      C √22 Correct Answer Incorrect Answer
      D √17 Correct Answer Incorrect Answer

      Solution

      Nine-digit number 89563x87y is divisible by 72, so the number is also divisible by 8 and 9. Divisibility law of 8 β‡’ A number divisible by 8 if its last three digits are divisible by 8. Divisibility law of 9 β‡’ A number is divisible by 9 if the sum of its digits is divisible by 9. 87y divisible by 8 if y = 2 Nine-digit number 89563x872 is divisible by 9 if the sum of its digits is divisible by 9. = 8+9+5+6+3+x+8+7+2 =48+x So, putting the value of x= 6 Now -√ (5x -4y) = √ (5Γ—6 – 4Γ—2) = √22.

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