Well, according to the rules of the kata its perfectly fine to cut people in half between months, or weeks. You cannot do this only between years.

Thank you, you have helped me to solve the problem that I was missing. People can't be cut in half

I'm not sure this makes sense. The note is about percents. The people who are having issues with a single test failing are struggling with percents. They're struggling with the case arguments: [1000 2 50 1214] thinking wrongly about decimals.

For people who are having issues with a single test case failing, be sure to read the note provided in the kata, which is provided as a hint for this particular issue (or other similar issues you may run into).