An electrical appliance will not work unless component QK does.Component QK's reliability is 0.95.Every other part of the appliance is 100% reliable.What would the reliability of the appliance be if a backup QK were added?
A).95
B).9975
C).9025
D).9205
E).9795

Question

Quizplus · Accepted Answer

The appliance will only work if component QK works, which has a reliability of 0.95. The probability of QK failing is 0.05. If a backup QK is added, the reliability of the appliance would be the probability of both components not failing, which would be the product of their individual reliabilities. 
Probability of first QK working = 0.95 
Probability of backup QK working = 0.95 
Probability of both QKs working = 0.95 x 0.95 = 0.9025 
Probability of both QKs failing = 0.05 x 0.05 = 0.0025 
Probability of at least one QK working = 1 - probability of both failing = 1 - 0.0025 = 0.9975 
Therefore, the reliability of the appliance with a backup QK would be 0.9975 or 99.75%.

An Electrical Appliance Will Not Work Unless Component QK Does