The table shows the marks of 60 students in a science exam. How many students failed the test given that the pass mark was 30?
As the pass mark was 30, the students that failed the test scored less than this. These students are represented in the following three groups: zero to nine marks, 10 to 19 marks, and 20 to 29 marks. There were three, 18, and 10 students in each of these groups, respectively. We therefore need to add three, 18, and 10. Three plus 18 is equal to 21. Adding 10 to this gives us 31.
We can therefore conclude that, of the 60 students who sat the science exam, 31 of them failed the test. As 31 of the students failed the test, we can see that 29 passed the test. Eight plus 15 plus six is equal to 29.