Probability Problem

[oxmamamia]

A bag contains 5 blue marbles, 4 white marbles and 6 red marbles. Three marbles are selected from the bag.

A) What is the probability they are all red?

B) What is the probability they are all the same color?

I'm confused as to how to find the number of combinations to complete this question, and to set it up for the equation P(n,r) divided by r! Please help!

 

[tkhunny]

p(red) = 1-p(not red) -- for some questions, all the other combinations are of no consequence.

p(all blue) = (5/15) * (4/14) * (3/13)

 

[lookagain]

A bag contains 5 blue marbles, 4 white marbles and 6 red marbles.
Three marbles are selected \(\displaystyle \ \text{without replacement **}} \\)from the bag.

B) What is the probability they are all the \(\displaystyle \text{same color}\)?

p(all blue) = (5/15) * (4/14) * (3/13) \(\displaystyle \text{or}\)

p(all white) = (4/15)(3/14)(2/13) or

p(all red) = (6/15)(5/14)(4/13)

--------------------------------------------------------------------------------------


p(all blue or all white or all red) =


\(\displaystyle \frac{5 \cdot 4 \cdot 3 \ + \ 4 \cdot 3 \cdot 2 \ + \ 6 \cdot 5 \cdot 4}{15 \cdot 14 \cdot 13}\)



\(\displaystyle ** \text{intended}\)