Trung bình cộng là: $\dfrac{2.3+3.m+5.8+6.7+7.2+8.9+10.n}{3+m+8+7+2+9+n}=6\\\to 174+3m+10n=6.(m+n+29)\\\to 3m+10n=6.(7+29)-174\\\to 3m+10n=42\\\text{Mà }m+n=7 \to m=7-n\\\to 3(7-n)+10n=42\\\to 21-3n+10n=42\\\to 7n=21\\\to n=3\\\to m=7-3=4\\\text{Vậy }m=4;\,n=3$