Em tham khảo nha:
\(\begin{array}{l}
1)\\
{\% ^{15}}N = 100 - 99,63 = 0,37\% \\
\overline {{M_N}} = 14 \times 99,63\% + 15 \times 0,37\% = 14,0037\\
2)\\
{\% ^{63}}Cu = \dfrac{{105}}{{105 + 245}} \times 100\% = 30\% \\
{\% ^{65}}Cu = 100 - 30 = 70\% \\
\overline {{M_{Cu}}} = 63 \times 30\% + 65 \times 70\% = 64,4\\
3)\\
{\% ^x}Ag = 100 - 44 = 56\% \\
\overline {{M_{Ag}}} = 107,88 \Leftrightarrow x \times 56\% + 109 \times 44\% = 107,88\\
\Rightarrow x = 107
\end{array}\)