Probability

Question

Jar A contains 3 red marbles and 5 green marbles. two marbles are drawn from the jar, one after the other, without replacement.

 

Find the probability that none are green.

 

Fund the probability that exactly 1 is green

Answer 1

For none are green: 

 

The probability that the first is red is 3/8, then the probability that the second is also red is 2/7 (one red already picked)

so 3/8 * 2/7 = 6/56 or 3/28

 

The probability that exactly one is green:

One way for this to happen is pick a green then a red, the probability of which is 5/8 * 3/7 = 15/56

The other way is to pick a red then a green, the probability of which is 3/8 * 5/7 = 15/56

since both ways will get you exactly one green, you add them together for 30/56 or 15/28