[SOLVED] expected value of marbles

questions:

a) We have 10 marbles in a bag: 7 red, 2 blue, 1 yellow. We randomly pull two marbles, with replacement. Find the expected value of the number of blue marbles pulled.


b) We have 10 marbles in a bag: 7 red, 2 blue, 1 yellow. We randomly pull two marbles, without replacement. Find the expected value of the number of blue marbles pulled.


-I can't figure this one out without being given an actual value on the blue marbles, any suggestions?

Try drawing a tree diagram
for a the prob would aways be choosing 10 marbles.

for b the first marble would be choosing out of 10 the second choosing out of 9(since you are not replacing)

hope this helps