http://www.ck12.org Chapter 2. Conditional Probability
Step 1:List what you know.
P(right the first time) =1
2
P(right the second time) =2
3
P(left the second time) = 1 −2
3
=
1
3
P(right the first time and left the second time) =1
2
×
1
3
P(right the first time and left the second time) =1
6
Step 2:Calculate the probability of choosing left as the second turn when right is chosen as the first turn.
P(left the second time|right the first time) =P(right the first time and left the second time)
P(right the first time)P(left the second time|right the first time) =1
6
1
2
P(left the second time|right the first time) =1
6
×
2
1
P(left the second time|right the first time) =2
6
P(left the second time|right the first time) =1
3
P(left the second time|right the first time) = 0. 333
P(left the second time|right the first time) =33%Step 3:Write your conclusion.
Therefore, the probability of choosing left as the second turn when right was chosen as the first turn is 33%.