Question "a box contain 6 red ,4 white,and 5 black balls.a person draws 4 balls from the bo at random.find the probabality that among the balls drawn there is at least one ball of each colour?
Answer 1. How many different selections are possible?
There are 6 red ,4 white,and 5 black balls.
a person draws 4 balls
First, pick any one, then one of remaining etc.
see how many combinations there are.
Hint: Picking up and arranging/order N things from T things can be done in T*(T-1)*(T-2)... (T-N+1) ways... this is called T P N.
Like (13 * 12 * 11 * 10 * 9)
Picking up and arranging/order N things from T things can be done in T*(T-1)*(T-2)... (T-N+1) ways/ N*(N-1)*(N-2)...*1 ways
.. this is called T C N.
Like (13 * 12 * 11 * 10 * 9)/(5*4*3*2*1)
2. Find out how many ways there is at least one ball of one colour.
So, pick one of each colour first. Then the fourth colour can be any of the other balls.
How many combinations is that?
