You got one half of the answer. You forgot the other part.
The question did not say find the probability of first marble being white and the second marble being Blue.

It jut asked for probability of picking up a white marble and a blue marble.

Probability of picking one white and one blue = P(W). P(B) + P (B). P(W)
2/10.5/9 + 5/10.2/9 = 1/9 + 1/9 = 2/9

bourne159 wrote:You got one half of the answer. You forgot the other part.
The question did not say find the probability of first marble being white and the second marble being Blue.

It jut asked for probability of picking up a white marble and a blue marble.

Probability of picking one white and one blue = P(W). P(B) + P (B). P(W)
2/10.5/9 + 5/10.2/9 = 1/9 + 1/9 = 2/9

Huh? What is the difference between "The probability of first marble being white and second being blue" and "Picking up a white and blue marble"? Those are the exact same questions in my mind. Both times, you're picking up two marbles. You want exactly one white. Then exactly one blue. What am I missing?

Stockmoose,

In probability the order is important. When asked what is the probability of getting a white marble and blue marble you have to find both
a) probability of first getting a white ball and then a blue ball +
b) probability of first getting a blue ball and then a white ball

bourne159 wrote:Stockmoose,

In probability the order is important. When asked what is the probability of getting a white marble and blue marble you have to find both
a) probability of first getting a white ball and then a blue ball +
b) probability of first getting a blue ball and then a white ball

Bourne,

What's the difference between "What is the probability of getting a white marble and blue marble" and "What is the probability of first picking a white marble, then picking a blue one? Can you explain how these are logically any different?

Stockmoose16 wrote:

bourne159 wrote:Stockmoose,

In probability the order is important. When asked what is the probability of getting a white marble and blue marble you have to find both
a) probability of first getting a white ball and then a blue ball +
b) probability of first getting a blue ball and then a white ball

Bourne,

What's the difference between "What is the probability of getting a white marble and blue marble" and "What is the probability of first picking a white marble, then picking a blue one? Can you explain how these are logically any different?

Bump. Somebody PLEASE help. I do not understand the logic here. I'm so confused.

Case 1:

In the question it says picking 2 marbles.

This means you could picked the white marble first and then the blue marble (ACHIEVED YOU END GOAL)

(or)

Pick the blue marble first and then the white marble (ACHIEVED YOUR END GOAL)

When its an OR you add the probablities


Case2:
If the problem reads "What is the probability of first picking a white marble, then picking a blue one"

IMO Then its simply 2/10*5/9

The OR situation does not happen since you have to pick the white marble first