Question

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. assume that we add a second back up for qk with reliability of 0.80 (this back up is the same as component qk but purchased from another manufacturer, so the reliability is different but it is also cheaper). what is the probability that the appliance does not work? (in this case, you have qk with reliability 0.95, qk first back up with reliability 0.95 and a second backup with reliability 0.80)

Answer 1

0.99 or 99%

Explanation:

This is actually much more simple than it sounds

Take 95% and add 80% of 5 because 5% of the time the QK piece will not work. 80% of 5 is 4. 95+4=99