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

Toán Lớp 5: 1. a) (5/7 : 3/4) x 2/5 + 131313/212121 b) (1 + 1/5) x (1 + 1/24) x (1 + 1/35) x…x (1 + 1/9999) 2.Tìm y, biết: a) y x 3 – y x 7/5

Tháng Hai 2, 2023 Toán học 2 Comments 0 views

Toán Lớp 5: 1. a) (5/7 : 3/4) x 2/5 + 131313/212121
b) (1 + 1/5) x (1 + 1/24) x (1 + 1/35) x…x (1 + 1/9999)
2.Tìm y, biết:
a) y x 3 – y x 7/5= 11,2
b) 1/3×5 + 1/5×7 + 1/7×9 +…+ 1/y + (y + 2)= 16/99 (y là số tự nhiên)

Comments ( 2 )

  1. tonhitruc
    tonhitruc
    2 Tháng Hai, 2023 at 4:49 chiều
    Reply
    1,
    a) ( 5/7 : 3/4 ) xx 2/5 + 131313/21212
    =20/21 xx 2/5 + 13/211
    = 8/21 + 13/21
    = 1
    b) ( 1 + 1/15 ) xx ( 1 + 1/24 ) xx ( 1 + 1/35 ) xx …. xx ( 1 + 1/9999 )
    = 16/15 xx 25/24 xx 36/35 xx …. xx 10000/9999
    = ( 16 xx 25 xx 36 xx …. xx 10000 )/( 15 xx 24 xx 35 xx …. xx 9999 )
    = ( 4 xx 4 xx 5 xx 5 xx 6 xx 6 xx …. xx  100 xx 100 )/( 3 xx 5 xx 4 xx 6 xx 5 xx 7 xx …. xx 99 xx 101 )
    = ( ( 4 xx 5 xx 6 xx …. xx 100 ) xx ( 4 xx 5 xx 6 xx …. xx 100 ) )/( ( 3 xx 4 xx 5 xx …. xx 99 ) xx ( 5 xx 6 xx 7 xx …. xx 101 ) )
    = ( 100 xx 4 )/( 3 xx 4 xx 101 )
    = 100/303
    2,
    a) y xx 3 – y xx 7/5 = 11,2
           y xx ( 3 – 7/5 ) = 11,2
                  y xx 8/5   = 11,2
                        y        = 11,2 : 8/5
                        y        = 7
    Vậy , y = 7 .
    b) 1/( 3 xx 5 ) + 1/( 5 xx 7 ) + 1/( 7 xx 9 ) + …. + 1/( y xx ( y + 2 ) ) = 16/99
    2 xx ( 1/( 3 xx 5 ) + 1/( 5 xx 7 ) + 1/( 7 xx 9 ) + …. + 1/( y xx ( y + 2 ) ) ) = 16/99 xx 2
    2/( 3 xx 5 ) + 2/( 5 xx 7 ) + 2/( 7 xx 9 ) + …. + 2/( y xx ( y + 2 ) ) = 32/99
    1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + …. + 1/y – 1/( y + 2 ) = 32/99
    1/3 – 1/( y + 2 ) = 32/99
    1/( y + 2 ) = 1/3 – 32/99
    1/( y + 2 ) = 1/99
    y + 2 = 99
    y = 99 – 2
    y = 97
    Vậy , y = 97 .

  2. tuanh
    tuanh
    2 Tháng Hai, 2023 at 4:49 chiều
    Reply
    Câu 1
    a ) ( 5/7 : 3/4 ) × 2/5 + 131313/212121
    = 20/21 × 2/5 + 13/21
    = 8/21 + 13/21
    = 1
    b ) ( 1 + 1/15 ) × ( 1 + 1/24 ) × ( 1 + 1/35 ) × … × ( 1 + 1/9999 )
    = 16/15 × 25/24 × 36/35 × … × 10000/9999
    = {16 × 25 × 36 × … × 10000}/{15 × 24 × 35 × … × 9999}
    = {4 × 4 × 5 × 5 × 6 × 6 × … × 100 × 100}/{3 × 5 × 4 × 6 × 5 × 7 × … × 99 × 101}
    = {4 × 100}/{3 × 4 × 101}
    = 100/303
    Bài 2
    a ) y × 3 – y × 7/5 = 11,2
    y × ( 3 – 7/5 ) = 11,2
    y × 1,6 = 11,2
              y = 11,2 : 1,6
              y = 7
    b ) 1/{3 × 5} + 1/{5 × 7} + 1/{7 × 9} + … + 1/{y × ( y + 2 )} = 16/99
    2 × ( 1/{3 × 5} + 1/{5 × 7} + 1/{7 × 9} + … + 1/{y × ( y + 2 )} = 16/99 × 2
    2/{3 × 5} + 2/{5 × 7} + 2/{7 × 9} + … + 2/{y × ( y + 2 )} = 32/99
    1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + … + 1/y – 1/{y + 2} = 32/99
    1/3 – 1/{y + 2} = 32/99
    1/{y + 2} = 1/3 – 32/99
    1/{y + 2} = 1/99
    => y + 2 = 99
                y = 99 – 2
                y = 97
    #dtkc

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

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