Simplify each of the expressions in parts (a) through (c) below.

1. $a b ( \frac { 1 } { a } + \frac { 1 } { b } )$ 

   Hint (a):

   Distribute $ab$.

   $\textit{ab}\left(\frac{1}{\textit{a}}+\frac{1}{\textit{b}}\right)=\frac{\textit{ab}}{\textit{a}}+\frac{\textit{ab}}{\textit{b}}$

   More Help (a):

   Simplify the expression.

   Answer (a):

   $b+a$

2. $c d ( \frac { 3 } { c } + \frac { 2 c } { d } )$ 

   Hint (b):

   See part (a).

   Answer (b):

   $3d+2c^2$

3. $x ( 1 - \frac { 1 } { x } )$ 

   Hint (c):

   See part (a).

4. What expression would go in the box in order to make the equation $\square ( \frac { 5 } { x } + \frac { 8 } { y } ) = 5 y + 8 x$ true?

   Hint (d):

   $\frac{5xy}{x}+\frac{8xy}{y}=5y +8x$