Thread: Maths probability distribution Im totally stuck

1. Maths probability distribution Im totally stuck

thanks

2. Originally Posted by elliegurl
hey I've just started doing maths at as level. I had my first statistics class last week and i am totally confused and stuck. I would be so grateful for any help.

Two questions that I have been given for homework for example are:
1. Three cards are selected at random, without replacement, from a shuffled pack of 52 playing cards. Using a tree diagram, find the probability distribution of the number of honours (A,KQ,J,10) obtained.

I did a tree diagram but didnt kno what to do next

Mr F says: Use it to calculate the probaility of 0, 1, 2 and 3 honours cards. I'd suggest finding a textbook or website that explains how to use a tree diagram to calculate the probability of a particular event occuring.

Another question is:

2. An electronic device produces an output of 0,1 or 3 volts, each time it is operated, with probabilities 1/2, 1/3, 1/6 respectively. The random varible X denotes the result of adding the outputs for two such devices which act independently.

a) Tabulate the possible values of X with corresponding probabilites

Mr F says: All the possible values of X are found by first adding two of the possible values of volts for all possible combinations:

0 + 0 = 0, 0 + 1 = 1, 0 + 3 = 3, 1 + 0 = 1, 1 + 1 = 2, 1 + 3 = 4, 3 + 0 = 3, 3 + 1 = 4, 3 + 3 = 6.

So the possible values of X are 0, 1, 2, 3, 4, 6.

Now use the above combinations to get the probability of each value.
eg. X = 0 requires getting two 0 voltages, 0 + 0: Pr(X = 0) = (1/2)(1/2) = 1/4.

eg. X = 1 requires 0 + 1 or 1 + 0: Pr(X = 1) = (1/2)(1/3) + (1/3)(1/2) = 1/3.
etc.

b) in 360 independent operations of the device, state on how many occasions you would expect the outcome to be 1 volt.

Mr F says: (360)(Pr(X = 1)).

I have no idea how to do them. We only did very basic questions in class. Any help would be great.

thanks ellie
..

3. thankyou so much