Never begin a sentence with a numeral. There is one exception: a numeral that identifies a calendar year.
When translating press releases or annual reports, we occasionally come across situations where we have to place the percentage at the beginning of the sentence.
E.g.: Twenty-eight percent of the participants passed the test last year.
Although this sentence is correct, it looks odd. Where possible, recast the sentence so that the numbers are expressed in figures.
Better: Last year, 28 percent of the participants passed the test.