NCERT Class XI Mathematics - Probability - Solutions

© examsnet.com
Question : 50
Total: 54
Out of 100 students, two sections of 40 and 60 are formed. If you and your friend are among the 100 students, what is the probability that
(a) you both enter the same section?
(b) you both enter the different sections?
Solution:  
Total favourable outcomes in which both the students are in same section of 40 students =
98
C38

Also, total favourable outcomes in which both the students are in same section of 60 students =
98
C58

(a) P(both students are in same section) =
98
C38
+
98
C58
100
C40

=
98!
38!60!
+
98!
58!40!
100!
40!60!
=
98![
1
38!60!
+
1
58!40!
]
100!
40!60!

=
98!×58!×38!
38!×60!×58!×40!
(40×39+60×59)
100!
40!60!
=
17
33

(b) P(both students are in different sections) = 1 -
17
33
=
16
33

© examsnet.com
Go to Question: