Ta có: `\overline{X} = \frac{10.25 + 9.42 + 8x + 7.15 + 6y}{100} = 8,69`
`\to \overline{X} = 733 + 8x + 6y = 869`
`\to \overline{X} = 8x + 6y = 136` ( `1` )
Mà `25 + 42 + x + 15 + y = 100`
`\to x + y = 18`
`\to x = 18 - y` ( `2` )
Thay ( `2` ) vào ( `1` ), ta có:
`\to 8.( 18 - y ) + 6y = 136`
`\to 144 -8y + 6y = 136`
`\to -2y = -8`
`\to y = 4`
`\to x = 14`
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