A lot of 20 bulbs contain 5 defective ones. If one bulb is drawn at random from the lot, find the probability that it is not defective.

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A lot of 20 bulbs contain 5 defective ones. If one bulb is drawn at random from the lot, find the probability that it is not defective.

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313

113

34

326

answer is B.

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Detailed Solution

Given that in a lot of 20 bulbs it contains 5 defective ones.
We need to find the probability that the bulb drawn is not defective.
Probability of an event E is defined as:

P (E) = \frac{Number of favorable outcomes}{Total number of possible outcomes}

Since there are 20 bulbs in a lot, therefore the total number of possible outcomes is 20.
Defective bulbs are 5. Therefore, non-defective bulbs are:

20 − 5 = 15

Hence, the number of favorable outcomes are 15.
Let

E

be the event that the bulb drawn is not defective.
Now, the probability of getting a non-defective bulb is:

P (E) = 1520

⇒ P (E) = 34

Thus, the probability of getting a non-defective bulb is

34

.
Therefore, option 2 is correct.

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