A teacher wanted to analyse the performance of two sections of students in a mathematics test of 100 marks. Looking at their performances, 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: $0-20,20-30, \ldots, 60-70$, 70 - 100. Then she formed the following table:
Find the probability that a student obtained marks 60 or above.
From the above question, the data of our interest is:
Total no. of students =90
Total no. of students who obtained marks 60 or above = 15+8 =23
P(a student obtains marks 60 or above) = 23/90
Ans: 23/90