Question
Six balls are drawn successively from an urn containing 7 red and 9 black balls. Tell whether or not the trials of drawing balls arc Bernoulli trials when after each drawn the ball drawn is (i) replaced (ii) not replaced in the urn.
Solution
The number of trials is finite. When the drawing is done with replacement, the probability of success (say, red ball) is 
which is same for all six trials (draws).
Hence, the drawing of balls with replacements are Bernoulli trails.
(ii) When the drawing is done without replacement, the probability of success (i.e., red ball) in first trial is
in 2nd trial is 
if the first ball drawn is red or 
if the first ball drawn is black and so on. Clearly, the probability of success is not same for all trials, hence the trials are not Bernoulli trials.
which is same for all six trials (draws).Hence, the drawing of balls with replacements are Bernoulli trails.
(ii) When the drawing is done without replacement, the probability of success (i.e., red ball) in first trial is
in 2nd trial is if the first ball drawn is red or if the first ball drawn is black and so on. Clearly, the probability of success is not same for all trials, hence the trials are not Bernoulli trials.
