Answer:
5
Step-by-step explanation:
Well, since the probability of blue pens is 1/2 you'll have to add the number of pens that is not blue. So that'll be 8+3 which equals 11. We currently have 6 blue pens and we need to add up the pens which will get 11. 11-6 equals 5, and that is the number of pens you will have to add.
Also, I'm not an expert at this so please check the work before you answer !