The functioning of a particular machine is dependent on two safety valves: A and B. The machine will operate fine as long as *one* of the safety valves is functioning properly. Both valves have a 10% chance of failure each. What is the chance that the machine will not break down?
A) 99%.
B) 90%.
C) 95%.
D) 80%.

Question

Quizplus · Accepted Answer

The chance that the machine will not break down is the chance that both valves are functioning properly. The chance that valve A is functioning properly is 90%, and the chance that valve B is functioning properly is also 90%. The chance that both valves are functioning properly is 90% * 90% = 81%. Therefore, the chance that the machine will not break down is 81%.

The Functioning of a Particular Machine Is Dependent on Two