# Chapter 4 - Probability - 4-3 Addition Rule - Basic Skills and Concepts: 37

0.09, the test is not so accurate.

#### Work Step by Step

We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$, and also $P(A\cup B)=P(A)+P(B)-P(A\cap B)$. Let A=false positive, B=false negative, then $P(A\cup B)=\frac{24}{300}+\frac{3}{300}-\frac{0}{300}=\frac{27}{300}=0.09.$ 0.09 is still a quite high number, so the test is not so accurate.

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