Question

Question 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:

Marks Number of student
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.

Class 9 - Math - Probability Page 284

Answer 1

Hi friend.

Total student are 90.

1)The number of student who obtained less than 20%marks in the mathematics test=7

So that, P(A Student obtaining less than 20%marks )

=7/90

2)No.of students who obtained marks 60 or above

=Student in 60-70+students above 70

=15+8=23

P(a student obtaining marks 60 and above )

=23/90

Hope helped!!!

Answer 2

Probability is the study of the chances of events happening.

Event:
A Possible outcome or combination of outcomes is called event.

The probability of happening our event always lies from 0 to 1.

The sum of all the probabilities of all possible outcomes of an experiment is 1.

Required probability=number of trials in which the event E has happened/Total number of trials .

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Solution;

Total numbers of students in a class= 90

(i) Numbers of students obtained less than 20%lies in the interval 0-20 in the mathematics test = 7

Required probability,P(less than 20%)= 7/90


(ii) Numbers of student obtained marks 60 or above lies in the marks interval 60-70 & 70-above = 15+8 = 23

Required probability,P(60-70 & 70-above) = 23/90

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Hope this will help you....