For you to set own custom number format in Excel, you first need a number in the cell that looks like this:

Note: The number can of course, be anything numerical.

Mark all the numbers.

Right click on the marked area (1), and choose format cells (2).

Click custom and set the customized number under type.

Examples:

To display 123456.78 as 123456.8 use ####.#

.123 as 0.1 use 0.# 

5.25 as 5 1/4 use # ???/???

Note: You can even format colors. Just write [color]