Ex15.1, 6
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… 60 − 70, 70 − 100. Then she formed the following table:
(i) Find the probability that a student obtained less than 20% in the mathematics test.
Total number of students = 90
Students with less than 20% marks = Students who have 0 – 20 marks
= 7
Probability that a student obtained less than 20%
= (𝑆𝑡𝑢𝑑𝑒𝑛𝑡𝑠 𝑤ℎ𝑜 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑙𝑒𝑠𝑠 𝑡ℎ𝑎𝑛 20% 𝑚𝑎𝑟𝑘𝑠)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑡𝑢𝑑𝑒𝑛𝑡𝑠)
= 7/90
Ex15.1, 6
(ii) Find the probability that a student obtained marks 60 or above.
Total number of students = 90
Students who have 60 marks or above
= Students who have 60 – 70 marks
+ Students who have 70 – above marks
= 15 + 8 = 23
Probability that a student obtained marks 60 or above.
= (𝑆𝑡𝑢𝑑𝑒𝑛𝑡𝑠 𝑤ℎ𝑜 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 60 𝑚𝑎𝑟𝑘𝑠 𝑜𝑟 𝑎𝑏𝑜𝑣𝑒)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑡𝑢𝑑𝑒𝑛𝑡𝑠)
= 23/90

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo

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