Express the following sums using sigma notation.

a$.7891011$

b$.4812162024$

c$.1^8{2}^8{3}^8{4}^8$

d$.\frac{1}{5}\frac{1}{6}\frac{1}{7}\frac{1}{8}$

a$.7891011={\displaystyle \underset{k=1}{\overset{5}{}}}$

b$.4812162024={\displaystyle \underset{k=1}{\overset{6}{}}}$

c$.1^8{2}^8{3}^8{4}^8={\displaystyle \underset{k=1}{\overset{4}{}}}$

d$.\frac{1}{5}\frac{1}{6}\frac{1}{7}\frac{1}{8}={\displaystyle \underset{k=1}{\overset{4}{}}}$