Unit digit of the square of 641

Here we will show you two ways of finding the unit digit of the square of 641. First, we will define what the unit digit of the square of 641 means. Next, we will find the unit digit of the square of 641 using the Rule Method, and then we will find the unit digit of the square of 641 using the Math Method.

The last digit (one digit) of the product you get when you multiply 641 by itself is the unit digit of the square of 641.

Rule Method
The unit digit of any square will never be 2, 3, 7, or 8. It can be only 0, 1, 4, 5, 6, or 9. Furthermore, the unit digit of the square of a number depends on its units digit. In other words, the unit digit of the square of 641 depends on 1, because that is the last digit in 641. Here are the rules:

Rule A) If the unit digit of a number is 0, then the unit digit of the square of that number is 0.

Rule B) If the unit digit of a number is 1 or 9, then the unit digit of the square of that number is 1.

Rule C) If the unit digit of a number is 2 or 8, then the unit digit of the square of that number is 4.

Rule D) If the unit digit of a number is 5, then the unit digit of the square of that number is 5.

Rule E) If the unit digit of a number is 4 or 6, then the unit digit of the square of that number is 6.

Rule F) If the unit digit of a number is 3 or 7, then the unit digit of the square of that number is 9.

The unit digit of 641 is 1, therefore Rule B applies, and the unit digit of the square of 641 is 1.

Unit digit of the square of 641 = 1

Math Method
The unit digit of the square of a number depends on its units digit with this method too. Here you multiply the unit digit of the number by itself, and then look at the unit digit of that product. Again, the unit digit of 641 is 1, so you multiply 1 by itself, and then look at the unit digit to get the answer once again:

1 × 1 = 1
Unit digit of 1 is 1.
Unit digit of the square of 641 = 1

Of course, instead of using either of the methods above, you can multiply 641 by itself if you have the time or a calculator, and then identify the unit digit to get the answer to the unit digit of the square of 641. We did that below to double-check that our answer is correct:

641 × 641 = 410881
Unit digit of 410881 is 1.
Unit digit of the square of 641 = 1

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