Multiply an even number by 6. The answer ends in the same digit as the even number halved! (6 x 4 = 24)
Same 3-digit number (like 333)? Add digits and divide the number by the sum. You always get 37!
Multiply a 2-digit number by 11. Separate the digits, add them, and put that sum between them. (72 x 11 = 792)
Use this sentence: How I wish I could calculate Pi. Count the number of letters in each word, and you get 3.141592.
9s x any number? Fold down that finger and count the fingers on both sides for the answer! (9 x 5 = 45)