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

Toán Lớp 5: Tính nhanh A) 25+26+27+28+29+30 B)25+26+27-…+49+50

Toán Lớp 5: Tính nhanh
A) 25+26+27+28+29+30
B)25+26+27…….+49+50

Comments ( 2 )

  1. a,25+26+27+28+29+30
    =(25+30)+(26+29)+(27+28)
    =55+55+55
    =55xx3
    =165
    b,25+26+27+…+49+50
    =(25+50)+(26+49)+…+(37+38)( có 12 cặp )
    =75+75+…+75
    =75xx12
    =900

  2. 25+26+27+28+29+30
    =(25+30)+(26+29)+(27+28)
    =55+55+55=55. 3=165
    25+26+27+…+49+50
    =(25+50)+(26+49)+…+(37+38)
    Tất cả ở tên có : [(50-25)+1]:2=13 (cặp)
    =75+75+75+…+75
    =75. 13=975 (cặp)
     

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

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