Misc 1
A box contains 10 red marbles, 20 blue marbles and 30 green marbles. 5 marbles are drawn from the box, what is the probability that
all will be blue?
5 marbles are to be chosen from 60 (10 red + 20 blue + 30 green)
Hence
n(S) = 60C5
Let A be the event that all are blue
Hence out of 20 blue marbles 5 will be chosen
n(A) = 20C5
P(A) = ( ) ( )
=
Misc 1
A box contains 10 red marbles, 20 blue marbles and 30 green marbles. 5 marbles are drawn from the box, what is the probability that
(ii) at least one will be green?
P(atleast one will be green)
= 1 P(none of marbles are green)
Lets first calculate probably that none of marbles are green
Let B be the event that none of marbles are green
If marble is not green, it will be red or blue
Hence, out of (20 + 10 = )30 marbles, 5 are to be selected
Hence
n(B) = 30C5
P(B) = ( ) ( )
= 30 5 60 5
Hence,
P(atleast one will be green) = 1 P(none of marbles are green)
= 1

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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