How to multiply easily

A.  Multiply any number by 4
      Example : 72 x 4 = 288

1. Double the number being multiplied by four. (7 x 2 = 144)
2. Double it again.(144 x 2 = 288)

B.  Multiply any number by 5

      Example : 27 x 5 = 135

1. Divide the number being multiplied by 2. (27 / 2 = 13.5)
2. Multiply step 1 by 10. (13.5 x 10 = 135)

C.  Multiply any number by 9

      Example : 52 x 9 = 468

1. Multiply the number by 10. (52 x 10 = 520)
2. Subtract the number from the result in step 1. (520 - 52 = 468)

D.  Multiply any two digit number by 11

      Example : 39 x 11 = 429

1. Add together the digits of the number being multiplied by 11. ( 3 + 9 = 12)
2. Place a zero between the two digits of the number being multiplied by 11. ( 309) 
3. Add the result from the step 1 to the zero in the number from step 2. Don't forget tocarry the 1 if there is one. (309 + 12 = 429)

E.  Multiply any number by 25
      Example : 44 x 25 = 1100

1. Multiply the number by 100 (44 x 100 = 4400)
2. Divide by 4 (4400 / 4 = 1100)

F.  Multiply any number by 99

     Example : 440 x 99 = 43560

1. Multiply the number by 100 (440 x 100 = 44000)
2. Subtract the number from the result in step 1 (44000 - 440 = 43560)

By : Stephanie Chungdinata
Source : Mathemagics