Answer:
Step-by-step explanation:
Given that a new drug test needs to be evaluated. The probability of a random person taking drugs is 4%. 
The drug test tested positive for a person not taking drugs 2% of the time. The drug test tested negative for a person taking drugs 1% of the time.
                           Tested positive     Tested negative       Total
Having drug               0.98                        0.02                  1.00
not hav drug               0.01                        0.99                   1.00
a)            the probability that a random person tests negative
= Prob ( really negative and test negative) + Prob (positive and test negative)

b) the probability that a person who tests negative is without any drug problems
= 