Mental Math Tricks

We have learned some mental math tricks at my school. Could you give me some tricks that would help me stand out at school? -- For Math Fun
Answer: Last year, we discovered a great book, "Secrets of Mental Math" by Arthur Benjamin, a professor of mathematics at Harvey Mudd College. You would probably enjoy reading this book. We also talked to him and discovered that you can actually learn to do some calculations faster in your head than by using a calculator.
One of his favorite feats of mental math is to multiply any two-digit number by 11. It is amazingly easy. For example, consider multiplying 45 x 11. All you have to do is add the digits 4 plus 5 and put the answer (9) between the 4 and 5. So 45 x 11 is equal to 495. However, you need to know more. If the sum of the digits is more than one digit, as it is in 47 x 11, you have another step. Add 4 plus 11. Put the last 1 in the middle and then add the other 1 to the 4, getting an answer of 517. Try multiplying 59 x 11. Your answer should be 649.