11．观察下列不等式
$1+\frac{1}{2^{2}}<\frac{3}{2}$
$1+\frac{1}{2^{2}}+\frac{1}{3^{3}}<\frac{5}{3}$,
$1+\frac{1}{2^{2}}+\frac{1}{3^{2}}+\frac{1}{4^{2}}<\frac{7}{4}$
照此规律，第五个不等式为 $\_\_\_\_$
参考答案
$1+\frac{1}{2^{2}}+\frac{1}{3^{2}}+\frac{1}{4^{2}}+\frac{1}{5^{2}}+\frac{1}{6^{2}}<\frac{11}{6}$ ．