SQUARING ANY NUMBER ENDING IN 1
Rule: First, square the number to the left of the units digit. Then double the number to the left of the units digit. Affix the units digit of this result to the square found in the first step. If the result is more than 9, add the part to the left of the units digit tothe square found in the first step. The units digit of the answer Is always 1.
Consider the following example: Square 251. The number to the left of the 1 is 25. Using Short Cut 45, we find the square of 25 is 625. Next, twice 25 is 50. Affix the zero in 50 to 625 and add the 5 to 625.
625 + 5 = 630
To which are affixed the 0 and the units digit (which is always 1).