# Thread: Probability that at least 1 was selected

1. ## Probability that at least 1 was selected

Having a bit of trouble with this one: Any help will be appreciated.

Suppose you are going to draw 2 jellyfish, without replacement, from a tank that contains 5 mushroom jellyfish and 3 cannonball jellyfish. Find the probability that at least 1 cannonball jellyfish will be selected.

a. 5/15
b. 9/14
c. 15/28
d. 1

2. Originally Posted by sweetkendra
Having a bit of trouble with this one: Any help will be appreciated.

Suppose you are going to draw 2 jellyfish, without replacement, from a tank that contains 5 mushroom jellyfish and 3 cannonball jellyfish. Find the probability that at least 1 cannonball jellyfish will be selected.

a. 5/15
b. 9/14
c. 15/28
d. 1
$Pr(X \geq 1) = 1 - Pr(X = 0)$.

$Pr(X = 0) = \frac{{3 \choose 0} \times {5 \choose 2}}{{8 \choose 2}}$, that is,

(the number of ways of choosing zero cannonball AND two mushroom0/(the number of ways of choosing two fish from eight).

3. ## Many thanks

Thank you for your help, I understand now.

Originally Posted by mr fantastic
$Pr(X \geq 1) = 1 - Pr(X = 0)$.

$Pr(X = 0) = \frac{{3 \choose 0} \times {5 \choose 2}}{{8 \choose 2}}$, that is,

(the number of ways of choosing zero cannonball AND two mushroom0/(the number of ways of choosing two fish from eight).

4. Originally Posted by sweetkendra
Thank you for your help, I understand now.
You're very welcome. Lovely manners