Here is a trick to quickly calculate the square of a number ending in "5": First, remove the last digit (the 5), and multiply what is left by itself plus 1. Let's take 75: 7*(7+1) = 56. These are the initial digits of the square. The last step is to add "25" to the end of the number. In our case we get 5625. Another example: 435^2: 43*(43+1) = 1892; we place 25 at the end and we get 189225, the square of 435.
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