On discovering that her family had a 70% risk of heart attack, Erin took a treadmill test to check her own potential of having a heart attack. The doctors told her that the reliability of the stress test is 67%. The test predicted that Erin will not have a heart attack. What is the probability after the test was taken that she will not have a heart attack?

A.) 0.099
B.) 0.201
C.) 0.231
D.) 0.469

Question

On discovering that her family had a 70% risk of heart attack, Erin took a treadmill test to check her own potential of having a heart attack. The doctors told her that the reliability of the stress test is 67%. The test predicted that Erin will not have a heart attack. What is the probability after the test was taken that she will not have a heart attack?

A.) 0.099
B.) 0.201
C.) 0.231
D.) 0.469

Vocaloid · Answer

“What is the probability after the test was taken that she will not have a heart attack?”

So we want the probability that the test:

1 accurately predicts that she won’t have a heart attack
And 
2 she won’t have a heart attack

Since her chance of having a heart attack is 70%, the probability of *not* having a heart attack is 30%

The test predicted her not having a heart attack with 67% accuracy

So multiply 30% * 67%