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Question

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?

Solution

The correct option is **B**

$4$

**Step 1: Explanation of the correct option**

Given that a number becomes a perfect square when we subtract $1$ from it.

We know that the unit digit of the square numbers will have $0,1,4,5,6,9$.

Thus, for all perfect squares, the unit digit will consist of only $0,1,4,5,6,9$ and none of the square numbers will end with $2,3,7,8$.

According to the question, a number becomes a perfect square when we subtract $1$ from it. Therefore the number's unit's digit cannot be $3,4,8,9$.

Therefore, option (B) is correct.

**Step 2: Explanation of the incorrect option**

Options (A), (C), and (D) do not give the correct answer.

Mathematics

Standard VIII

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