A number becomes a perfect square when we subtract 1 from it. Which of the given options CANNOT be the last digit of that number? a) 2 b) 4 c) 5 d) 0​

If the number had a 2 as its last digit, then subtracting 1 would make it a perfect square. So the new number would end with digit 1 which can be a perfect square. Hence, 2 can be the answer.

If we consider the numbers 1 to 10, the squares of these numbers are

1, 4, 9, 16, 25, 36, 49, 64, 81 and 100.

This helps us understand that all perfect square numbers end in either 1, 4, 5, 6, 9 or 0. A number that does not end in any of the above numbers is not a perfect square number.

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