NCERT Class X Chapter 14: Probability Exercise 14.1 Question (17)
NCERT Class X Chapter 14: Probability Exercise 14.1 Question 17
Question:
(i) A lot of 20 bulbs contain 4 defective ones. One bulb is drawn at random from the lot. What is the probability that this bulb is defective?
(ii) Suppose the bulb drawn in (i) is not defective and is not replaced. Now one bulb is drawn at random from the rest. What is the probability that this bulb is not defective ?
Given:
Total number of bulbs = 20
Number of defective bulbs = 4
To Find:
(i) Probability that the bulb drawn is defective.
(ii) Probability that the second bulb drawn is not defective, given the first bulb was not defective and not replaced.
Formula:
Probability = Favorable Outcomes Total Outcomes
Solution:
(i) Probability that the bulb drawn is defective:
Total number of outcomes = 20
Favorable outcomes (defective bulbs) = 4
Probability (defective) =
4
20
=
1
5
(ii) Probability that the second bulb is not defective:
After drawing one non-defective bulb and not replacing, total number of bulbs = 19
Number of defective bulbs = 4
Number of non-defective bulbs remaining = 19 - 4 = 15
Probability (not defective) =
Number of non-defective bulbs
Total number of bulbs
Probability (not defective) =
15
19
Result:
(i) The probability that the bulb drawn is defective is
1
5
(ii) The probability that the second bulb drawn is not defective is
15
19
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