How to multiply any number by 9 Example: 55 x  9 = 495 Put a zero (0) after 55 :  550 Subtract the original number (55) :  550 - 55 = 495 How to multiply any number by 5 Take half the multiplicand nd multiply it by 10. Example:  34 x 5 = 170 34 x 5 = 17 (half of 34) x 10 = 170 More examples: 27 x 5 = 13.5 (half of 27) x 10 = 135 44 x 5 = 22 (half of 44) x 10 =  220 93 x 5 = 46.5 (half of 93) x 10 = 465 How to multiply any number by 15 Take half of the multiplicand, add it to the multiplicand.  (19 + 38) Multiply the sum total x 10.  (57 x 10) Example: 38 x 15 = 570 38 x 15 =  38 + 19 (half of 38)  = 57 57 x 10 = 570 How to multiply any number by 25 Take the multiplicand and divide it by 4  (26 \ 4) Multiply the quotient by 100  (6 x 100) Example:  24 x 25 = 600 24 x 25 = (24 \ 4) x 100 = 6 x 100 = 600