Answer: 0.21
Step-by-step explanation:
Given : A bag contains one red pen, four black pens, and three blue pens.
Total pens = 1+4+3=8
Probability that first pen was black = [tex]\dfrac{\text{Number of black pens}}{\text{Total pens}}=\dfrac{4}{8}=0.5[/tex]
Probability that the next second pen was black given that the first was black = [tex]\dfrac{\text{Number of black pens left}}{\text{Total pens left}}=\frac{3}{7}[/tex]
Using conditional probability formula , the probability that a black pen is chosen first and then another black pen is chosen = (Probability that first pen was black) x (Probability that the next second pen was black given that the first was black)
= [tex]0.5\times\dfrac{3}{7}=0.214285714286\apptox0.21[/tex]
Hence, the correct answer is 0.21.
