Answer:
1/14
Explanation:
The number of ways or combinations in which we can select x objects from a group of n can be calculated as:
[tex]\text{nCx}=\frac{n!}{x!(n-x)!}[/tex]
So, if we are going to select 3 pens from the drawer that contains 8 pens, the number of possibilities is:
[tex]8C3=\frac{8!}{3!(8-3)!}=\frac{8!}{3!\cdot5!^{}}=56[/tex]
Then, if we didn't end up with a pen that works is because we select the three pens from the 4 that didn't work. In this case, the number of possibilities is:
[tex]4C3=\frac{4!}{3!(4-3)!}=\frac{4!}{3!\cdot1!}=4[/tex]
Therefore, the probability required is equal to the ratio of these quantities:
[tex]P=\frac{4}{56}=\frac{1}{14}[/tex]
So, the answer is 1/14