Write the following expressions using summation notation.  

1. $\frac { 1 } { 3 } + \frac { 1 } { 4 } + \frac { 1 } { 5 } + \ldots + \frac { 1 } { 11 }$ 

   Hint (a):

   Write an expression for the linear sequence $3, 4, 5, ...$ .

2. $\frac { 1 } { 4 } + \frac { 1 } { 6 } + \frac { 1 } { 8 } + \ldots \frac { 1 } { 30 }$ 

   Hint (b):

   Write an expression for the linear sequence $4, 6, 8, ...$ .

3. $1+8+27+\dots+216$ 

   Hint (c):

   These are cubic numbers.