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9. Each of the 4 engines on an airplane functions correctly on a given flight wi

ID: 3303971 • Letter: 9

Question

9. Each of the 4 engines on an airplane functions correctly on a given flight with probability 0.99, and the engines function independently of each other. Below is a table indicating the probability that the plane can make a safe landing under various scenarios: 0 0 (a) What is the probability that only 1 of the engines functions correctly? b) What is the probability that at least 2 of the engines function correctly? (c) What is the probability that the plane makes a safe landing? (d) Given that the flight makes a safe landing, what is the probability that it lands with only 1 of the engines functioning correctly?

Explanation / Answer

(a) Probability that an engine functions correctly = 0.99

=> Probability that an engine does not function correctly = 1 - 0.99 = 0.01

There are 4 ways of choosing the correctly functioning engine.

=> Probability that only 1 engine performs correctly = 4 * 0.99 * 0.13

= 0.00000396.

(b) Let us first calculate the probability that no engine functions correctly

= (0.01)4

= 0.00000001

=> Probability that zero or one engine functions correctly

= 0.00000396 + 0.00000001

= 0.00000397

=> Probability that atleast 2 engines function correctly

= 1 - 0.00000397

= 0.99999603.

(c) Probability that the plane makes a safe landing

= 0.00000396 * 0.5 + 0.99999603

= 0.99999801.

(d) Probability that a safely landed plane lands with only 1 engine functioning correctly

= 0.00000396 * 0.5 / 0.99999801

= 0.00000198.