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

Toán Lớp 6: 1 1/2+1 1/6+1 1/12+-.+1 1/90

Toán Lớp 6: 1 1/2+1 1/6+1 1/12+…..+1 1/90

Comments ( 2 )

  1. 1 1/2 + 1 1/6 + 1 1/12 + … + 1 1/90
    = \underbrace{1 + 1 + 1 + … + 1}_{9 số 1} + ( 1/2 + 1/6 + 1/12 + … + 1/90 )
    = 1 × 9 + ( 1/{1 × 2} + 1/{2 × 3} + 1/{3 × 4} + … + 1/{9 × 10} )
    = 9 + ( 1/1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + … + 1/9 – 1/10 )
    = 9 + ( 1/1 – 1/10 )
    = 9 + 9/10
    = 99/10
    #dtkc
     

  2. #huy
    1 1/2+1 1/6+1 1/12+…..+1 1/90
    =(1+1+1+…+1)+(1/2+1/6+1/12+…+1/90)
    =1+(1/90-1/2):1+1
    =1+23/45
    =68/45
     

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