Given:
Sarah has 1 red cube, 1 green cube, 1 purple cube, and 1 black cube.
Sarah picks two items from the bag without replacement.
We need to determine the probability that she will pick a red cube and then a black cube.
Probability:
The probability to pick a red cube is
![P(R)=(1)/(4)](https://img.qammunity.org/2021/formulas/mathematics/high-school/ite6q8ljx8hvzfkvbupxla24nq2repodk0.png)
The probability to pick a black cube without replacement is
![P(B)=(1)/(3)](https://img.qammunity.org/2021/formulas/mathematics/high-school/gyfvuo2em5dsqmtt30kpxvr8hryo69sol2.png)
The probability to pick a red cube and then a black cube is given by
![P(RB)=P(R) \cdot P(B)](https://img.qammunity.org/2021/formulas/mathematics/high-school/u7d9s4xhdvc7fjgbw97xgyxl6hi38i497b.png)
Substituting the values, we have;
![P(RB)=(1)/(4) \cdot (1)/(3)](https://img.qammunity.org/2021/formulas/mathematics/high-school/uwmjt992an91om0dbkxg1xcle0iruazpb1.png)
![P(RB)=(1)/(12)](https://img.qammunity.org/2021/formulas/mathematics/high-school/23oz3ic94q8mpyboodgwze8b8zavd12kx1.png)
Thus, the probability that Sarah will pick a red cube and then a black cube is
![(1)/(12)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/gqlvfd89gc8mt75qu8rabv5c42tn5s46y6.png)