Students are taught to write out the numbers zero to nine unless they represent a measurement. Some students are taught to write out the numbers zero to one hundred. My sister has three cats. It is 3 degrees today. I received an 8.5 on my test. For university papers and journalism, the rules are more complicated. Here is one detailed set of rules: https://www.grammarbook.com/numbers/numbers.asp

In the UK, we give the mark as a number out of the total, so here it would be written 8.5/10 and said "Eight point five out of ten". Edit: You can also write 8.50/10 but it would still be said "Eight point five out of ten".

Hi there, It’s very, very unusual to write marks in words. I have only ever received a mark as just that: 8.5. 8.50 (eight point fifty) sounds to an English speaker as if you’re talking about £8.50 in money. If you have to write it in words, eight point five (8.5) is the way to go. But as I say, I’ve never seen marks written out as words, only as numbers. Hope this helps!