1. Is it better to write a number in one way rather than another? 
For example in decimal form rather than as a percentage.

Although each form represents the same number, it is often more CONVENIENT to use on form rather than another.
e.g. When talking about a wage rise or an exam mark, we often use a percentage.
If we are measuring the length of a piece of wood we use decimals rather than fractions


2. How is the fraction "one third" written as a decimal?

When doing the division 1.0000 ÷ 3, the answer 0.3333... is obtained.
To indicate that the "3" repeats forever a point is placed above the first 3 i.e. 

3. Using a calculator, how is a fraction changed into a decimal?

By division. Divide the bottom number into the top one.

4. How are percentages changed into decimals or fractions?

Changing percentages into decimals or fractions always involves either multiplying or dividing by 100.

5. Is it acceptable to write fractions such as "one half" as  ?

While  is equivalent to final answers should always be given in their simplest form.