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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 5: Tính thuận tiện: 3/4 x 8/9 x 15/16 x – x 99/100=

Toán Lớp 5: Tính thuận tiện:
3/4 x 8/9 x 15/16 x …. x 99/100=

Comments ( 2 )

  1. 3/4 x 8/9 x 15/16 x …… x 99/x100
    =(1 x 3) x (2 x 4) x (3 x 5) x (4 x 6) x (6 x 7) x (7 x 8) …. x (9 x 11) 
        (2 x 2) x (3 x 3) x (4 x 4) x (5 x 5) x (6 x 6) x ( 7 x 7) x  ….. x (10 x 10)
    = (1 x 2 x 3 x 4 x 5 x  … x 9) x (3 x 4 x 5 x 6 x 7 x …. 11)
         (2 x 3 x 4 x ………. x 10) x ( 2 x 3 x 4 x 5 x 6 x 7 x …. 10)
      =( 1x 11):( 10 x 2)
       = 11
           20

  2. Giải : 
     = 3/4 .  x 8/9 .  x 15/16  x …. x 99/100 .
    = $\frac{1 .  x 2 x 3 x … x 9 }{2 x 3 x 4 x .. x 10   }$  x $\frac{3 . 4 . 5 . … . 11}{2 . 3 . 4. … . 10}$ 
    = 1/10 x 11/2
    = 11/20

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222-9+11+12:2*14+14 = ? ( )