Squaring numbers that end in 5

You know that 5 x 5 = 25. However, do you realize that the square of any number that ends with 5, will also contains 25 in the last 2 digits.



Example 1:

25 x 25 = 625

Steps:

Remove the last digit. We get 2.

1 + 2 = 3 <-- Add 1.

3 x 2 = 6 <-- Multiply 2 times the result.

6 and 25 give 625 <-- Concatenate the result with 25.

Example 2:

205 x 205 = 42025

Steps:

Remove the last digit. We get 20.

1 + 20 = 21 <-- Add 1.

21 x 20 = 420 <-- Multiply 20 times the result.

420 and 25 give 42025 <-- Concatenate the result with 25.

Example 3:

315 x 315 = 99225

Steps:

Remove the last digit. We get 31.

1 + 31 = 32 <-- Add 1.

32 x 31 = 992<-- Multiply 31 times the result.

992 and 25 give 99225 <-- Concatenate the result with 25.

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