2.1. Real numbers $a, b, c, d, e$ are such that $a+b+c+d+e=8$ and $a^{2}+b^{2}+c^{2}+d^{2}+e^{2}=16$. Find the maximum possible value of $e$.
2.1. We have $(8-e)^{2}=(a+b+c+d)^{2} \leqslant 4\left(a^{2}+b^{2}+c^{2}+d^{2}\right)=4\left(16-e^{2}\right)$, so that $5 e^{2} \leqslant 16 e, e \leqslant 16 / 5$. Equality is achieved when $e=16 / 5, a=b=c=d=6 / 5$.