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John is eating jellybeans.In his bag of jellybeans he has 2 red, 2 green and 1 black jellybean left.Find the probability that the next 2 jellybeans he eats are both red?

 May 12, 2017
 #1
avatar+470 
+1

1 out of 5 + 1 out of 4 

9 out of 20

or 0.45%

 

im not sure tho

 May 12, 2017
 #2
avatar+22343 
+1

John is eating jellybeans.In his bag of jellybeans he has 2 red, 2 green and 1 black jellybean left.

Find the probability that the next 2 jellybeans he eats are both red?

 

Method 1:

probability  2 red \( = \frac{2}{5} \cdot \frac{1}{4} = \frac{2}{20} = \frac{1}{10} = 0.1\quad (10 \% )\)

 

Method 2:

probability  2 red

\(\begin{array}{|rcll|} \hline &= & \frac{\binom{2}{2}_{red}\binom{2}{0}_{green}\binom{1}{0}_{black}}{\binom52} \\ &=& \frac{1\cdot 1 \cdot 1 } { \frac52\cdot \frac41} \\ &=& \frac{2}{20} \\ &=& \frac{1}{10} \\ &=& 0.1\quad (10 \% ) \\ \hline \end{array}\)

 

laugh

 May 12, 2017

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