Academic Writing: Avoid using a Number at the Beginning of a Sentence
Our four main style guides, The Chicago Manual of Style, The AP Stylebook, APA Publication Manual, and the MLA Handbook, all agree that numbers should be spelled out in full form at the beginning of sentences. So the rule of thumb in academic writing is to avoid beginning a sentence with a number. Instead, either find a way to rephrase the sentence so that the number does not appear at the beginning, or spell it out in full.
However, there might be discrepancies amongst style guides, even among the basic ones. The AP Stylebook, for example, allows numerals denoting years (e.g., 2020) to be used at the beginning of sentences. It also permits the use of acronyms or words that begin with a number to appear at the beginning of a sentence (e.g., 3D movie).
Correct: Ninety four participants answered the survey.
Also correct: A total of 94 participants answered the survey.
Incorrect: 94 participants answered the survey.