A teacher wanted to analysis the performance of two sections of students in a mathematics test of 100 marks. Looking performance, she found that a few students got under 20 marks and a few got 70 marks or above. So she decided to group them into intervals of varying sizes as follows :
0-20, 20-30, ....., 60-70, 70-100. Then she formed the following table :
`|{:("Marks"," Number of students"),(0-20," 7"),(20-30," 10"),(30-40," 10"),(40-50," 20"),(50-60," 20"),(60-70," 15"),(70-"above"," 8"),("Total"," 90"):}|`
(i) Find the probability that a student obtained less than `20%` in the mathematics test.
(ii) Find the probability that a student obtained marks 60 or above .

Explanation

Please refer to video to see the histogram for the given data table.