How do I write a percentage, ex 70% and decimal 2.4 in a formal paper: number or written words?
The number of the percentage should be written as a number. Whether to write out the word "percent" depends on the context- whether it is scientific or not. If you are writing a science paper, write 70%, but if the paper is for, say, a business class, write 70 percent.
Decimals have no special rules, just write them out as numbers- 2.4 kilograms.
See the Purdue OWL Numbers page for more examples.
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