IMO B...but is B [1 - (0.94^10)] because thats what I am getting.

solution : consider in 10 minutes space

1 light bulb can go off P = 0.06

so, P that the lightbulb does not go off = 1-0.06 =.94

now we have 10 lightbulbs. Their functioning properly forms a mutually exclusive set of events.

therefore, P that all of them function properly = .94 * .94 (10 times) = .94^10

now, for the whole system to trip even 1 faulty bulb is enough.

therefore, we need P(at least one trips)

which is P(at least one) = 1 - P(none trip) = 1 - P(all function properly) = 1 - 0.94^10

Ans B

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