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Least perfect square number, exactly divisible by 21, 36 and 56 is_________?

Correct answer: D. 7056

  • A. 3600
  • B. 504
  • C. 441
  • D. 7056

Explanation

The LCM of 21, 36 and 56 is 2^3 x 3^2 x 7 = 504. To make this a perfect square, the odd power of 2 must be supplied by another factor of 2, and the factor 7 must be squared, so the least square is 504 x 14 = 7056. The likely mistake is option b, 504, which is divisible by all three numbers but is not a perfect square.

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