Unit digit of the square of 11909

Here we will show you two ways of finding the unit digit of the square of 11909. First, we will define what the unit digit of the square of 11909 means. Next, we will find the unit digit of the square of 11909 using the Rule Method, and then we will find the unit digit of the square of 11909 using the Math Method.

The last digit (one digit) of the product you get when you multiply 11909 by itself is the unit digit of the square of 11909.

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 11909 depends on 9, because that is the last digit in 11909. 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 11909 is 9, therefore Rule B applies, and the unit digit of the square of 11909 is 1.

Unit digit of the square of 11909 = 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 11909 is 9, so you multiply 9 by itself, and then look at the unit digit to get the answer once again:

9 × 9 = 81
Unit digit of 81 is 1.
Unit digit of the square of 11909 = 1

Of course, instead of using either of the methods above, you can multiply 11909 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 11909. We did that below to double-check that our answer is correct:

11909 × 11909 = 141824281
Unit digit of 141824281 is 1.
Unit digit of the square of 11909 = 1

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