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Đáp án `+` Giải thích các bước giải:

Bài `7.`

`a)`

`17.5 + 7.17 - 16.12`

`= 85+7.17-16.12`

`= 85+119-16.12`

`= 85+119-192`

`=12.`

`b)`

`27.97-27.17+80.73`

`= 2619-27.17+80.73`

`= 2619-459+80.73`

`= 2619-459+5840`

`=8000.`

`c)`

`29.93-62.29+71.31`

`= 2697 -62.29+71.31`

`= 2697-1798+71.31`

`= 2697-1798+2201`

`= 3100.`

`d)`

`17.125-17.20-105.7`

`= 2125-17.20-105.7`

`= 2125-340-105.7`

`= 2125-340-735`

`= 1050.`

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Bài `8.`

`a)`

`53 . 39+47.39-53.21-47.21`

`= 2067 + 47 . 39-53 .21 -47.21`

`= 2067+1833-53.21-47.21`

`= 2067+1833-1113-47.21`

`= 2066+1833-1113-987`

`= 1800.`

`b)`

`28.56-28.46+72.55-72.45`

`= 1568-28.46+72.55-72.45`

`= 1568-1288+72.55-72.45`

`= 1568-1288+3960-72.45`

`= 1568-1288+3960-3240`

`= 1000.`