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Question

Which of the following can't be the unit's digit of a perfect square?

This question was previously asked in
SSC CGL 2017 (Tier 1) Previous Year Paper (16-Aug-2017) (Shift 1)
The correct answer is

8

The units digit of \(n^2\) depends only on the units digit of \(n\). Squaring 0-9 gives units digits \(\{0,1,4,9,6,5,6,9,4,1\}\), so a perfect square can end only in 0, 1, 4, 5, 6 or 9.

Digits 2, 3, 7 and 8 never appear. Among the given options, 8 is the impossible units digit.

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Important Questions from Square and Square Root

  1. \(\sqrt{\frac{1.21\times0.9}{1.1\times0.11}}\) is equal to : 
  2. What is the square root of 123454321?

  3. With what number should you multiply 117 to make it a perfect square.

  4. The square root of 2025 is

  5. Which of the following numbers is not a perfect square?

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