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

Toán Lớp 5: Tính nhanh tổng sau : 1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90

Tháng Bảy 31, 2022 Toán học 2 Comments 0 views

Toán Lớp 5: Tính nhanh tổng sau :
1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90

Comments ( 2 )

  1. truonganhthi
    truonganhthi
    31 Tháng Bảy, 2022 at 6:15 sáng
    Reply
    1/2+5/6+(11)/(12)+(19)/(20)+(29)/(30)+(41)/(42)+(55)/(56)+(71)/(72)+(89)/(90)

    =1-1/2+1-1/6+1-1/(12)+1-1/(20)+1-1/(30)+1-1/(42)+1-1/(56)+1-1/(72)+1-1/(90)

    =9 – (1/2+1/6+1/(12)+1/(20)+1/(30)+1/(42)+1/(56)+1/(72)+1/(90))

    =9 – [1/(1.2)+1/(2.3)+1/(3.4)+1/(4.5)+1/(5.6)+1/(6.7)+1/(7.8)+1/(8.9)+1/(9.10)]

    =9 – ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/(10))

    =9 – (1 – 1/(10))

    = 9 – 9/(10)

    = (81)/(10)

  2. danvanthu
    danvanthu
    31 Tháng Bảy, 2022 at 6:15 sáng
    Reply
    = ( 1 − 1/2 ) + ( 1 − 1/6 ) + ( 1 − 1/12 ) + ... + ( 1 − 1/90 )
    = ( 1 + 1 + ... + 1 ) − ( 1/2 + 1/6 + ...+ 1/90 )
    = 9 − ( 1/1 x 2 + 1/2 x 3+ ... + 1/9 x 10 )
    = 9 − ( 1 − 1/2 + 1/2−1/3 + ... + 1/9 − 1/10 )
    = 9 − ( 1 − 1/10 )
    = 9 − 9/10
    = 81/10

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

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