This is a quick trick for finding the square of two-digit numbers. For example, if you've got something like 33*33, that's a tough product to find.

To more easily find the product, just round one of the numbers to the nearest 10, to make the problem 30*33. Then, because you took away 3 from the first number, add 3 to the other number to make the problem 30*36. Then the multiplication problem is easier, because 30*36 can be found by multiplying 3*36 to get 108, and then adding back the 0 to get 1,080.

Then, because you changed each number by 3, add back 3^2=9 to that result, and you can then say that 33*33=1,089.

Want to learn more about Pre-Algebra? I have a step-by-step course for that. 😃