Use the symbol % to express percent in scientific and technical writing, except when writing numbers at the beginning of a sentence. When you write out the word, use the form percent instead of the older form per cent.
Only 3% of the systems crashed during the test period.
Three percent of the systems crashed during
the test period.
In nontechnical writing, use the word percent rather than the symbol %.
The population has increased 1.42 percent during the past ten years.
The word percentage refers to a general result or portion.
The percentage of system failures was below the limit set for the prototype.