$Đáp$ $Án$ + $giải$ $thích$:
`B`ài 5:
`a`) `75`.`20,9` `+` `5²`. `20,9`
`=` (`75`+`25`) . `20,9`
`=` `100` . `20,9`
`=` `2090`
`b`) `86`. `15` `+` `150`. `1,4`
`=` `86`. `15` `+` `15`. `1,4`
`=` (`86`+`14`) . `15`
`=` `100` . `15`
`=` `1500`
`e`) `85`. `12,7` `+` `5.3.12,7`
`=` `12,7` . (`85`+`15`)
`=` `12,7` . `100`
`=` `1270`
`f`) `8,4` . `84,5` `+` `840`. `0,155`
`=` `8,4` . `84,5` `+` `8,4`. `100`. `0,155`
`=` `8,4` . `84,5` `+` `8,4`. `15,5`
`=` `8,4` . (`84,5` + `15,5`)
`=` `8,4` . `100`
`=` `840`
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