Answer:
D. 2/7
Step-by-step explanation:
The probability is calculate as a division between the number of ways in which Andrew will be selected and karen will not and the total ways in which they can select 4 people from a group of 8 volunteers.
The number of ways in which they can select 4 people from a group of 8 volunteers can be calculated using:
Where nCk give as the number of ways in which we can form groups of k elements from a group of n elements.
So, if we replace n by 8 and k by 4, we get:
Then, there are 70 ways to select 4 people from a group of 8 volunteers.
At the same way, the number of ways in which Andrew will be selected and karen will not can be calculate replacing n by 6 and k by 3 in the same equation as:
We replace n by 6 because from the 8 volunteers, Andrew is going to be selected and Karen will not, so, the people that affect the result are just the 6 remaining volunteers. Also, k is equal to 3 because Andrew is already selected and we just need to select 3 more people.
Finally, the probability is: