Merging partially duplicate lines

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I    9     A    B    0.25   6
I    21    B    A    1      6
I    33    C    C    0.5    2
I    40    D    D    1      2
I    56    A    E    1      2

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I    9     A    B    0.30   8
I    21    B    A    1      6
I    33    C    C    1      2
I    40    D    D    1      5

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I    9     A    B    0.275   14
I    21    B    A    1       12
I    33    C    C    0.75    4
I    40    D    D    1       7
I    56    A    E    1       2

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