Assuming use of a standard US keyboard, a Windows PC, and a desired symbol of "÷"; hold the "Alt" key and press "246" on the number pad. This must be done with the number pad, located on the right, not the row of numbers above the letters.
If using a laptop or keyboard without a number pad, the "Fn" key needs to be held in addition to the "Alt" key to use the correct set of numbers. With the "Alt" and "Fn" keys held down, pressing "k u o" will send "246" and create the "÷" symbol. Tables of available symbols and their numeric codes are found in the Character Map underneath Start, Program Files, Accessories and then System Tools.