00:01
In this problem we have been given that if we roll a fair four -sided die and the result is one or two, we roll once more, otherwise we stop.
00:08
What is the probability that the sum total of our rolls is at least four? so here let us first assume this event ai, which means result of the first role.
00:21
So here we must understand that result of the first role, let's say, is i.
00:26
Then probability of ai will be equals to 1 over 4, where i can be equals to 1 .2 .3 .4.
00:39
Now let's say there is another event b.
00:42
So b is sum of total is at least 4.
00:49
Hence we can say that it is given that a1 is some total will be greater than 4.
00:58
So we can write some total greater than equals to 4 if the second row results in 3 or 4 which happens with how much probability.
01:11
It happens with probability of 1 over 2 and what is happening we can write if the second so for this very event the probability is half...