Probability works for any given number, so we will assume there are 100 students. Of those 100, 85 of them studied. Since 75% of 85 students passed, we will multiply 85 by 0.75. This gives us 60. So of the students who studied, 60 of them passed. Of the 15 students that didn’t study, 30 percent passed. So we multiply 15 by 0.3. This gives us 4.5 students. Add up 60 and 4.5, and you get 64.5. The probability of passing is 64.5%. If you want to round up, it would be 65%. If you want to round down, it would be 64%. But the most precise answer is 64.5%.
