So I got this homework about statistics and the sentence is quite confusing.
"The result of the math exam in a school is normally distributed with an average of $74$ and a standard deviation of $7.9$. If the top $10\%$ got A in their report and the next $25\%$ got B, what is the lowest possible score of getting B?
So what confusing me is the next thing. Does it mean just $25\%$ of all so the lowest possible score of B is at the top $10\% + 25\% = 35\%$ (or $65\%$ from the bottom), or $25\%$ after A is excluded (or $75\%$ of $90\%$ = $67.5\%$ from the bottom)?
If it resembles "percentiles" like 90th percentile is top 10 percent, then 80th being the next 10 percent we'd have 80th percentile from 80 percent to 90 percent and so on. Then for your example, if they were doing it that way, you'd be looking for the mark m such that exactly 35 percent got m percent or better.
Note that if they were always going down some percent less than 100 percent of what was so far remaining, then the whole wouldn't get used up in a finite number of steps, which would seem odd (at least to me).