Since you should never begin a sentence with a numeral, you should first try to reword the sentence. If you find it unwieldy to reorder your words, spell out the number:

Seventy-six percent of the class barely passed the final, 18% flunked miserably, and 6% burst into tears.

Normally you shouldn’t mix words and numerals, but you can make an exception to avoid having a number at the start of a sentence.