Gọi số vở của tổ 1 là a,tổ 2 là b,tổ 3 là c
Theo đề bài ta có:
\(\Rightarrow\left\{{}\begin{matrix}a+b+c=150\\b=\dfrac{a+c}{2}\\a-c=30\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a+b+c=150\Rightarrow b=150-a-c\\b=\dfrac{a+c}{2}\end{matrix}\right.\)
\(\Rightarrow\dfrac{a+c}{2}=150-a-c\)
\(\Rightarrow\dfrac{1}{2}a+\dfrac{1}{2}c=150-a-c\)
\(\Rightarrow150=\dfrac{1}{2}a+\dfrac{1}{2}c+a+c\)
\(\Rightarrow150=\dfrac{3}{2}a+\dfrac{3}{2}c=\dfrac{3}{2}\left(a+c\right)\)
\(\Rightarrow a+c=100\)
\(\Rightarrow b=50\)
\(\Rightarrow\left\{{}\begin{matrix}a+c=100\\a-c=30\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a+c-a+c=100-30\Rightarrow2c=70\Rightarrow c=35\\a=30+35=65\end{matrix}\right.\)
