Question

4 defective pens are accidentally mixed with 16 good ones. It is not possible to just look at a pen and tell whether or not it is defective. One pen is drawn at random from the lot. What is the probability that the pen is defective?  

Answer 1

Total number of pens = 4 + 16 = 20 

Total possible outcomes = 20  

Number of defective pens = 4 

P(defective pen) = `4/20 = 1/5`