Here's a trick to help you square two-digit numbers in your head. It still requires you to do some multiplication and some addition, but the operations are generally easier than what you'd have to do if you just multiplied the two numbers together.

1. Given your two-digit number, find the closest number that ends with a zero. For example, to square 16, your closest number that ends with zero is 20. If you get a number like 15, it doesn't matter which way you go - either 10 or 20 will work.

2. Take the difference between your original value and your selected number ending in zero and add or subtract that to your original number so that you are moving away from your number that ends in zero. For example, if your number is 16, your number ending in zero is 20. The difference is 4, so subtract 4 from 16 to get 12. If your original number was 14, your number ending in zero would be 10, the difference would still be 4, but you'd add 4 to 14 to get 18.

3. Take this new number and multiple it by your number ending in zero. As examples, for 16 you'd multiply 12 * 20 to get 240 (that's pretty easy to do in your head). For 14, you'd mutliply 18 * 10 to get 180 (again, easy to do in your head).

4. To this result you just got, add the square of the difference you had in step 2 (the difference between your original number and the number ending in zero). In both our examples, the difference is 4, the square is 16, so we'd add this to out result and that is the final answer.

Yeah, it sounds crazy but this always works. Here are some more examples just so that it's clear

25 squared: 30 * 20 + 25 = 625
32 squared: 30 * 34 + 4 = 1024
18 squared: 20 * 16 + 4 = 324
81 squared: 80 * 82 + 1 = 6561

Using this trick, it is almost always easier to find the square in this fashion since you never need to multiple two-digit numbers together.