Question

There are 3 white marbles and 7 blue marbles in a bag. Jamie will randomly pick two marbles out of the bag without replacing the first one. What is the probability of Jamie picking a white marble and then a blue marble?

Answer 1

We know the number of all ways to take one marble and then take another marble is: 10x9=90
The first time, Jamie wants to pick a white and the ways is: 3
Now we have only 9 marble with 2 white and 7 blues, she has 7 ways to take a blue . So, she has 3x7=21 ways to take what she wants.
And we do the division 21:90=7/30. and that is the answer