\(\frac{1}{a}\)-\(\frac{1}{b}\)=\(\frac{2}{143}\);b-a=2 \(\frac{a}{3}\)+\(\frac{1}{6}\)=\(\frac{2}{b}\)

\(pt\Leftrightarrow\frac{29-x}{21}+1+\frac{27-x}{23}+1+...=0\)

\(\Leftrightarrow\frac{50-x}{21}+\frac{50-x}{23}+\frac{50-x}{25}+\frac{50-x}{27}+\frac{50-x}{29}=0\)

\(\Leftrightarrow\left(50-x\right)\left(\frac{1}{21}+\frac{1}{23}+\frac{1}{25}+\frac{1}{27}+\frac{1}{29}\right)=0\)

Do \(\frac{1}{21}+\frac{1}{23}+\frac{1}{25}+\frac{1}{27}+\frac{1}{29}>0\) nên 50 - x = 0 hay x = 50.

mỗi bạn đc số cây bút là :

12: 4 = 3 ( cây bút )

đs = 3cây bút