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.

Explanation

Total number of marbles in the box .=10+20+30=60.
i) 5 blue marbles drawn from 20 blue marbles in . ^20 C_5. ways 5 marbles drawn from 60 marbles in . ^60 C_5. ways.
.therefore. Probehility of all will be blue .= ^20 C_5/ ^60 C_5..
ii) 5 green marbles drawn from 30 green marbles in . ^30 C_5. ways.
.therefore. Probability of atleast one will be green .=1- ^30 C_5/ ^60 C_5.