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

Made by

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.