You can quickly square a 3-digit number when the middle number (number in the tens place) is zero in about 4 seconds by following this trick.
Example #1
(604)2
Step 1
Square 6 and write it down on the left: 62 = 36
36
Step 2
Square 4 and write it down on the right side of 36: 42 = 16
36 16
Notice how we leave a space between 36 and 16.
Step 3
Multiply 2 by the product of the number in the ones place and the number in the hundreds place.
2 × 6 × 4 = 48
Step 4
Write 48 between 36 and 16 and you are done.
(604)2 = 364816
When working on step 2, if after squaring the digit in the ones place you get a number less than 10, just add a zero on the left. Example #2 below shows how to do this!
Example #2
(903)2
Step 1
Square 9 and write it down on the left: 92 = 81
81
Step 2
Square 3: 32 = 9
Since 9 is smaller than 10, put a zero on the left of it and write everything on the right side of 81.
81 09
Step 3
Multiply 2 by the product of the number in the ones place and the number in the hundreds place.
2 × 3 × 9 = 54
Step 4
Write 54 between 81 and 09 and you are done.
(903)2 = 815409