Feminine vs masculine numbers
What makes a number feminine or masculine Ex ochocientas ochento y uno
1 Answer
If you are counting female people, female animals, or feminine gender non living things, you use the feminine form "--cientas" and also change "uno" to "una" when appropriate.
Your number example is incorrect. It should be: ochocientas ochenta y una sillas (en el auditorio, por exemplo).
The number "ochenta" doesn't change. It always has the "a" ending.