Ta có : X = \(\frac{2.10+5.4+9n+10}{10+4+n+1}=\frac{20+20+9n+10}{15+n}=\frac{50+9n}{15+n}\)

Mà đầu bài cho : X = 6,8

Nên : \(\frac{50+9n}{15+n}=6,8\)

\(\Leftrightarrow50+9n=102+6,8n\)

\(\Leftrightarrow102-50=9n-6,8n\)

\(\Leftrightarrow2,2x=52\)

Sai đề ak bạn

Ta ó: \(\frac{6.5+8a+9.3+10.1}{5+a+3+1}=7,5\)

\(\Rightarrow\frac{67+8a}{9+a}=7,5\)

\(\Rightarrow67+8a=7,5\left(9+a\right)\)

\(\Rightarrow67+8a=67,5+7,5a\)

\(\Rightarrow8a-7,5a=67,5-67\)

=> 0,5a = 0,5

=> a = 1

$\overline{x} = 6,8 \iff \dfrac{5\cdot 2 + 6 \cdot 5 + 9 \cdot n + 10 \cdot 1}{2 + 5 + n + 1} = 6,8$

$\iff \dfrac{50 + 9n}{8 + n} = 6,8$

$\iff 50 + 9n = 6,8(8 + n)$

$\iff 9n - 6,8n = 6,8 \cdot 8 - 50$

$\iff 2,2n = 4,4$

$\iff n = 2$ (N)

Vậy $n = 2$

cam on ban nhieu lam

em ko biết

a là cái j vậy bn

a là 10 

mình tính kết quả rồi đó

Trung bình cộng:

\(\overline{X}=\frac{2.3+3m+5.8+6.7+7.2+8.9+10n}{3+m+8+7+2+9+n}=\frac{6+40+42+14+72+3m+3n+7n}{29+\left(m+n\right)}\)

\(\overline{X}=\frac{174+3\left(m+n\right)+7n}{29+7}=\frac{174+3.7+7n}{36}=\frac{195+7n}{36}\)

Mà \(\overline{X}=6\)

\(\Rightarrow\frac{195+7n}{36}=6\)\(\Rightarrow195+7n=36.6\)\(\Rightarrow195+7n=216\)\(\Rightarrow7n=216-195\)\(\Rightarrow7n=21\)\(\Rightarrow n=3\)

Ta có: m + n = 7 => m + 3 = 7 => m = 4