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

Toán Lớp 5: 3/6+3/12+3/20+3/30+3/42+3/56+3/72

Home/ Toán Lớp 5: 3/6+3/12+3/20+3/30+3/42+3/56+3/72

Toán Lớp 5: 3/6+3/12+3/20+3/30+3/42+3/56+3/72

Tháng Chín 11, 2022 Toán học 1 Comment 0 views

Toán Lớp 5: 3/6+3/12+3/20+3/30+3/42+3/56+3/72

Comments ( 1 )

  1. giahan44
    giahan44
    11 Tháng Chín, 2022 at 6:44 chiều
    Reply
    Gọi tổng 3/6+3/12+3/20+3/30+3/56+3/72 là A, ta có:
    A= 3/6+3/12+3/20+3/30+3/56+3/72
    A= 3/2×3+3/3×4+3/4×5+3/5×6+3/6×7+3/7×8+3/8×9
    A:3= 1/2×3+1/3×4+1/4×5+1/5×6+1/6×7+1/7×8+1/8×9
    A:3= 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 (vì 1/2×3=1/6; 1/2-1/3=1/6)
    =>A:3= 1/2-1/9 => A:3= 7/18 =>A=7×3/18 =>A=21/18=7/6
    Vậy tổng 3/6+3/12+3/20+3/30+3/56+3/72 bằng 7/6

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

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