total no. of outcomes= 2^5, (as for each day they're two option either rain or no rain)havok wrote:If the probability of rain on any given day in City X is 50 percent, what is the probability that it rains on exactly 3 days in a 5-day period?
now we want 3 exact rainy days, let rainy day be represented by x and non rain days be represented by y,
therefore we need to arrange 5 objects of which 3 are of one type and 2 are of others, hence required arrangements would be 5!/2!*3!=10;
therefore required probability is 10/2^5=5/16..!!!
