Stockmoose16 wrote:I desperately need someone to explain the difference between these two questions:

In a bag of 10 marbles, there are 6 white, 4 blue:

1) "What is the probability of getting a white marble and blue marble"

2) "What is the probability of first picking a white marble, then picking a blue one?

These two questions sound exactly the same to me, but according to my GMAT book, have two different answers. Can someone explain the difference between the two questions in layman's terms?

parallel_chase wrote:

Stockmoose16 wrote:I desperately need someone to explain the difference between these two questions:

In a bag of 10 marbles, there are 6 white, 4 blue:

1) "What is the probability of getting a white marble and blue marble"

2) "What is the probability of first picking a white marble, then picking a blue one?

These two questions sound exactly the same to me, but according to my GMAT book, have two different answers. Can someone explain the difference between the two questions in layman's terms?

"What is the probability of getting a white marble and blue marble"

= 6/10 * 4/9 + 4/10 * 6/9

= 4/15 + 4/15 = 8/15 [here order of picking marbles is not mentioned, therefore you have consider both the possibilities]

"What is the probability of first picking a white marble, then picking a blue one?

= 6/10*4/9 = 4/15


Hope this helps.

Stockmoose16 wrote: Can you please explain why the order makes any difference? (effectively doubling the answer?)